UK Standard Visitor Visa combines many UK short-term visas, including a UK visitor visa for tourists, the most common one, which is why the two are often used interchangeably. You can apply for a UK Standard Visitor Visa if:

You go to the UK for tourism, for example, during annual leave or Christmas holidays.
You are visiting your friends or relatives living in the UK.
You are volunteering with a registered charity for up to 30 days.
You are passing through the UK on the way to another country (‘in transit’).
You have a medical condition that needs private treatment in the UK, or you are donating an organ.
You are attending a conference or a business meeting or getting training.
You are visiting a sport event, for example, a football game or a boxing match.
You are coming to the UK as an entertainer, artist or musician to give a concert, perform a play or hold an exhibition.
You are doing research or accompanying students on a study-abroad programme.
You are coming to the UK as a doctor or a dentist to act as a medical representative or an observer.
You are taking the Professional and Linguistic Assessment Board (PLAB) test or sitting the Objective Structured Clinical Examination (OSCE), which are British qualifications to obtain medical practice.
You want to get married in the UK and you have no intention to stay or settle in the country (you will need to apply for a special type of the UK Visitor Visa – Marriage Visitor visa).

If you want to get a UK visitor visa, you must be able to show to the Home Office the following:

You have reasonable grounds for visiting the country – it is better if you can provide evidence.
You will leave the country before your visa expires. In other words, you will leave the UK once your purpose is accomplished – you have spent your holidays in the country, you have visited your British friends or relatives, you have taken your exams, completed your training course, attended a sport event, etc.
You have enough funds to support yourself and your dependants during your trip and you are not going to ask British authorities for help. You might have financial support from a third party, for example, the exhibition organiser, if you are an artist.
You have enough funds to pay for your return or onward journey, if you are passing through the UK to another country.
You will not live in the UK through frequent or successive visits, or make the UK your main home.
You will only do the permitted activities if you are coming to the UK on a short-term business trip.

A valid passport with a blank page for your Standard Visitor visa or another travel document.
Evidence that you will be able to support yourself during your trip, for example, a bank statement.
Evidence of the purpose of your visit to the UK, especially if you are coming to study, to receive medical treatment or as an academic.
Evidence that you will leave the UK in 6 months at the latest.
Documents to support the information you provided in your visa application such as evidence of your income sources, ties to the country of residence, invitations and letters from the receiving party.
You must provide certified translations of any documents that are not in English

We are UK regulated immigration advisers
We will officially represent you before the Home Office
We will assess your case and evaluate your chances of success
We will analyse potential risks of visa refusal
We will prepare all the necessary evidence, documents, cover letters
We will provide certified translations of any documents
We will help you to fill in your visa application taking into account all the requirements
We guarantee legal support and advice at all stages

Usually, your UK Standard Visitor visa is valid for six months only, but you may be permitted to stay longer in the following cases:

If you have come to the UK to receive medical treatment.
If you are an academic, your UK Visitor visa can be extended for up to 12 months in total, the same applying to your family members.
If you are a medical graduate doing a clinical internship or re-sitting a Professional and Linguistic Assessment Board (PLAB) test.
Besides, if you plan to have several short-term trips to the UK in the coming years, you should consider applying for a long-term UK Standard Visitor visa for two, five or even ten years. Note that if you visit the UK regularly and stay for long periods (longer than 6 months a year), the Home Office may consider this an attempt to settle in the country and will cancel your visa.

If you have a degree at the highest academic level (PhD or higher), you have been working in your field of expertise for a long time and are not going to occupy a permanent teaching post at a British university, you can apply for a UK Standard Visitor visa valid for up to 12 months.

However, an application fee will be higher:

£190, if you apply through a visa application centre in your country;
£993, if you come to the UK on a Standard Visitor visa valid for up to six months and decide to extend your visa for up to 12 months in total.
As you can see, if you want to minimise costs, it will be a good idea to apply for a UK Visitor visa valid for up to 12 months before your visit, instead of paying extra costs for staying longer when you are already in the UK.

The following information must be provided in an online application for a UK Standard Visitor visa:

Arrival and departures dates of planned travel to the UK.
Where you will stay during your visit.
The approximate cost of your trip.
Your current home address and how long you have lived there.
Your parents’ names and dates of birth.
Your annual income.
Detailed information about any criminal, civil or immigration offences you may have committed.
Depending on the circumstances, you might also be required to provide the following information to get a UK Standard Visitor visa:

Details of your trips abroad for the past ten years.
Your employer’s address and telephone number.
Name, date of birth and passport number of your unmarried partner or spouse.
Name and address of your sponsor paying for your trip to the UK.
Names, addresses and passport numbers of all family members living in the UK, if any.