Ds (NDSTT/NDSL) downloading help !!?

okk,, so iv got a nintendo ds and iv had it for years am my mums (old) BF used to download all the games for me so now that they've split i want new games on my ds iv got everything you need for it i just don't know which websites or how to get them actually downloaded on to your pc can anyone help will this is there any software you need or anything and ps i don't want to pay for anyone of the software xx thank you xx and any cheeky comments will be reported x