Are they saw or already stained? Is the stain already on them lighter or darker than you want? Need more info please.
If they already have a finish on them, it will have to be removed, Alvera. You will need to use a chemical stripper or sand them.
I assume the cabinets are bare untreated timber? Then use any wood stain available from DIY store. If not then you would need to strip them to the bare wood, or if already stained and you want them to be darker, you could use a Gel stain on top once you have removed the sealer by rubbing down with fine sandpaper.
Hi Alvera, here's some good information from a "pro". Don't skip on the prep work as that's what makes the entire project turn out well.