Furniture, Wood and Cabinetry Finishing - help on redo on wood doors

Have wood doors that need to be sanded, restained and whatever else you have to do when you need to maintain wood doors. Have never done this before and would like to do ourselves instead of paying a ton of money for someone else to do. Can anybody give some type of instruction or pointers on how to start the process. We need to take care of this soon since the doors are showing some wear. The doors also run along the back of our house where our pool is. Any help or guidance would be appreciated.

Are the doors interior or exterior doors? If exterior, are they exposed to sun and rain?

A lot depends on their current condition. If they are in decent shape it may only be a matter of scuff sanding and applying another coat of poly/varnish. Really bad doors might need stripping, sanding, staining and refinishing.

Are the doors interior or exterior doors? If exterior, are they exposed to sun and rain?
They are exterior doors that run along the back of our house where we have a screened pool enclosure. One set of doors does get quite a bit of sun during most of the day. The doors are like night and day the side that is on the inside is fine and the side that is outside is the opposite.

Exterior doors should be painted with spar urathane - Minwax Helmsman is one such poly.

Since the doors are weathered you should first sand them down. After sanding wipe them down with a wet thinner rag, while wet you will get an idea what they would look like with just poly applied. If they look ok apply 2 coats of spar urathane. If they need more attention - really bad would need to be stripped and refinished. If bad in just a few areas you can restain the bad areas. This isn't as easy as it sounds. It is best to try a stain that is a little too light first because you don't want to over darken the affected area. All stain will appear darker when coated with poly.

Doors that are subjected to a lot of weather often require recoating on a yearly basis.