You will not be able to apply for your Student visa from within the UK unless you are already in the UK with a Student visa and you meet specific academic progression conditions, or you have a different visa type which allows you to switch to the Student route.
You must read the section 'Can I apply in the UK?' to understand the limited circumstances in which you can apply for a visa within the UK. You MUST NOT come to the UK as a Standard Visitor or without a visa (non-visa national/Electronic Visa Waiver), as you will not be able to make a Student visa application from within the UK and you will not be permitted to start your course.