Many people go to the UK in summer to study English. Typically, they enrol in a language school for a fortnight (=two weeks) or even longer, and attend language classes in the morning. In the afternoon, there is often a choice between supplementary (= extra) lessons, or social activities, such as trips to museums or places of local interest, or sport activities. The school will probably also book your accommodation.
Maybe you will stay with a local family on a full-board (= accommodation and all meals included) or half-board (= accommodation plus breakfast and dinner) basis, or perhaps you will stay in student accommodation, such as a hall of residence (= specially-built accommodation for students attending English universities).
Before you start your English course, you'll probably need to do a placement test, which will assess your language level. If you're attending a business English course, you'll probably also do a needs analysis, which pinpoints the areas of business English that you need to work on.
Most language schools offer a range of courses. For instance, you might decide to have your lessons in a small group, or you might prefer a one-to-one or individual course. Schools also offer exam-preparation courses (for the Cambridge or TOEFL exams) as well as YL (young learner = children) courses and ESP (English for Specific Purposes) courses.
Your teacher should be TEFL-qualified, which means that he or she has undergone specific training to teach English as a foreign language. He or she should be sensitive to your problems or needs, as well as able to manage the classroom effectively and to provide a range of learning activities.
However, it's also true to say that you "get out what you put in": the harder you study, and the more you take advantage of being in an English-speaking country, the faster you will improve your English.