A 64 year old woman do it yourselfer.
Assuming this is a prefabricated vanity such as you'd purchase at one of the big box stores then it's a pretty simple attachment.
1) It'd be ideal if you could locate the studs behind the sheetrock and be able to place the vanity where you could use wood screws to tie into these. Studs are normally placed on 16 inch centers, but my experience with bathrooms is that the location where you want to install it does not accomodate that.
2) Assuming that it doesn't, then you'll have to obtain plastic screw inserts from a local hardware store.
3) You'll need to drill some holes. The size will be indicated on the packaging for the inserts, if you need to use inserts.
4) If you don't need to use inserts then you'll need to drill holes for the screws that are just a tad smaller than the actual screw.
5) and this should be above #1. Have some help.