You may want to take a friend with you. When you get there, you will probably need to go to the receptionist first, to book in. The receptionist can also help you with any forms you have to sign. You may have to sit in a waiting room before you see the optician. This is often boring, but there are usually magazines and comics to look at.
Opticians do eye tests.
This means they look at your eyes to check they are healthy. You should have an eye test every two years, or more often if the optician says you need it. Most people with learning difficulties can get a free eye test. You will only have to pay if you work, or have lots of savings. The optician will find the best way to help you see better.