As a general rule, cloth nappies fit slightly lower on baby's back than disposables, so the back of the nappy usually lines up with the top of the pelvis.
As you bring the nappy up between baby's legs, you will need to tuck the sides in so that the elastic is high up baby's leg, close to their crotch. We call this the 'knicker line'.
When you bring the outside wings over baby's tummy to close the nappy, you should pull them up towards baby's shoulder/upper arm then across. This fixes gaps where the knicker line goes around baby's bum.
All the absorbent insides of the nappy should be covered by the waterproof outer.
Nappy should fit tightly, but not too tight. Marks like 'sock marks' are fine. Baby will tell you if its too tight. Until you feel expert, please always double check the elastic fit; you should be able to run a finger between the nappy and the baby, but there should not be any gaps.
All liners/nappies/boosters/wraps are interchangable but some do fit better than others. If the waterproof is built-in you do not need a wrap over the top.
If the nappy or wrap has two rows of closure poppers, you may find it easier to close the lower ones first to ensure a good fit round the legs, before closing the waist poppers.
If the nappy or wrap has 'riser' poppers to change its size, start with it on the smallest setting.
Photo credits: S. Malik, Go Real, S. Ojar, S .Mairease, E. Pollard, S. Calcutt Cheadle, H. Gad, C. Bromley-Morgans, B. Farrow.