Know Your Employment Rights in Your First Real Job

Your contract said three months probation and twenty-five days holiday and not much else. This covers what your employer is legally required to tell you in writing, what your rights are during probation versus after it, how holiday accrues from day one, what statutory sick pay is actually worth, and three rights that frequently surprise people who thought they were on thin ice.

I have just started a new job in the UK and I want to understand my employment rights. Explain:
1. The difference between employed, self-employed, and worker status and how to tell which one I am
2. What my employer is legally required to give me in writing and by when
3. My rights during probation: what changes and what does not
4. Holiday entitlement: how it accrues, when I can take it, and what happens to it if I leave
5. Sick pay: statutory sick pay, when it kicks in, and what my employer can and cannot ask for
6. Three rights I almost certainly have that I might not know about

Assume I am an employee (not self-employed) in England or Wales. Keep it in plain English.