Calcium questions

Hi everyone! My friend is getting a Leopard gecko in about a week and she's asked me to help her make sure her setup is ok and she has everything before she brings him home. She's new to reptiles and I own a BP so she thought I'd be able to help. Well I know nothing about Leos except from the research I've done.
Can someone explain the whole calcium thing? I've read that you should have both calcium with d3 and without because d3 can be bad in large doses? I'm confused as to what she needs to buy for this and how often to dust food with what calcium? We saw a powder in the store today that was specifically for leopard geckos, also one that was a multivitamin without d3. What should she buy? Help!

Thanks,
Robyn

I use Rep-Cal pure calcium, calcium w/D3 and Herptivite for my Leo's.
When they were babies/juvies I dusted with the pure calcium or vitamins every other day (each, so 3 days of calcium and 3 days of vits) and the D3 once a week. I never tried the 'all in one' supplements so can't comment on them.
I always leave a milk cap of pure calcium in the tanks, they do lick at it.