it depends on your grip also
theres 3 main grips:
forward (hands forwards)
reverse (hands backwards)
and eagle (hard to explain but these are hard to do)
Palms facing inwards at shoulder width should be the easiest to get started. (Palms facing outward puts more load on the Triceps, and is much harder, but is the only way to go if you're a Rockclimber)
If you cannot yet do a complete lift, you can always do negative reps - I use them as an exhaustion exercise if I'm doing chins.
Get a bench, place it under your chinup bar and stand on it. You should be up at the height you would be if you had just done a chin up. Grip the bar, raise your feet off the bench, and slowly lower yourself until your arms are almost straight. That's 1 negative rep. Do a few sets and see how you feel.
When you're ready to make things harder, instead of just curling your legs up underneath you when you take the weight on your arms, bring your legs straight out infront of you, so you're in a L-shape (bend at the waist, keep knees straight). Great for your abs. You'll often need to face outwards from the chinup bar if it is wall or machine mounted, so you have space to raise your legs.