If you are not such an accomplished handyman, yet you still would like the satisfaction of making your own writing desk, one option open to you is to buy the un-assembled pieces and put them together. Another option that requires a little more work, but that perhaps would be a little more satisfying to some is to buy an old desk and refinish it.
Old writing desks are usually fairly easy to find at second hand furniture shops or at garage sales. If you let the word spread that you are interested in acquiring one, oftentimes friends or relatives will be able to put you in touch with someone who has one too.
The first thing to decide is where you are going to work on the project. You need a place where you can leave the desk and your tools and brushes out, as it will need time to dry between applications of stain and varnish. The garage is often a great place to work, or a spare bedroom or even a garden shed if you have one on your property. It will need to be under cover, unless you are sure that it will not rain during the time you are working on it.
Your first step, once you have the writing desk, is to sand it down to strip off all of the old varnish and stain. This is best accomplished using an electric sander and fine sandpaper to strip the stain or paint off. If you do not have an electric sander just do it by hand, it will take longer of course but it does just as good a job as using an electric sander.
After you have finished your first (and any subsequent) sanding, wipe off the piece of furniture with a damp rag so that it is clean and dust free. Once it is clean from dust and sand you should apply your first coat of stain. This is usually best applied with a brush although you can even apply it with a rag if there are places you cannot get to properly with a brush. Follow the instructions on the stain regarding how long to leave it before applying your second and further coats. When you have arrived at the appearance you want it is time to finish up with a final layer of varnish which can be either brushed on or sprayed on.
If you do not want to go to all the trouble of first sanding down the writing desk you could also look into the possibility of buying an unfinished desk. All you would need to do with that desk is the staining and varnishing, to accomplish the same purpose.