WE40 will clean off some oils and fouling and replace water if the gun got wet. If that is all you have on hand, it will work in a pinch. But it's not a very good long term lub or protector. If you want one product, go with a CLP. Most easy to find is Breakfree. That stands for Clean - Lubricate - Protect. The idea and fromulation was developed for the military to make it easy to take care of guns in the feild. CLP works pretty well, except for metal fouling in your barrels. It will remove some, but there are other products to do that.
I'd say a good starter kit for cleaning is some Breakfree, some Hoppes #9 solvent, some Hoppes gun oil, and depeding on the gun, some grease like Slide Glide, Rig +P or TW25B. Of course a cleaning rod, brushes, jags and patches will be needed to take care of the inside of the bore. Bore snakes work will too if there is not too much fouling in the barrel. I use those on my .22's for a quick clean up after shooting a couple hundred rounds.
I use Shooter's Choice MC#7 to clean my firearms. Then I'll lubricate them with Hoppe's 9 oil or Rem oil. You'll find that there are a lot of different solvents & lubricants, along with different type patches & brushes. You'll have to try them your self to know which one's work best for you.
I also like to use Berchwood Casey GUN SCRUBBER Synthetic Safe Cleaner on really dirting firearms. Make sure you wear eye protection, though.