I can't afford a car let alone insurance so whats the point of learning to drive now ?

Its best to learn as soon as you can. You never know when you will suddenly need that full driving licence to get to work, a new job, college or university.

Your insurance is usually cheaper the longer you have held a full licence, even if you have not driven since your test.

Because of DSA test waiting times it usually takes at least about 8 weeks to get a driving test appointment, and if you don't pass first time another 8 weeks for a retest.

Beware of anyone claiming to get you a test date in less than this time, it is rarely possible. 

It is possible to learn to drive within about one or two weeks, but then you still have to wait about 8 weeks for the test appointment.

Do I need to pass the theory test before learning to drive ?

NO.

In fact it is best to have a few lessons with an instructor first who will help teach you the requirements for the theory tests and do mock tests. Make sure your instructor offers this facility.