Go to Megaton disarm the Nuke for Lucas Simms but don't ask for any money when you agree to do it. When you disarm the nuke he'll give you a house in Megaton. Now you have a base of operations.
As for money you get it the same way you do in every Bethesda open world rpg. Kill bad guys sell their stuff. Springvale Elementary which is right near where you exit the vault has some low level raiders you can take out. Just strip them down of all their weapons and armor, and when you run out of inventory space start repairing stuff. Also find and hang on to every prewar book you find you'll need them.
You should also do the Wasteland Survivor guide quest for Moira Brown in Megaton. It will net you some useful items. Always try to do the bonus optional objectives. Do the radiation one first it's the easiest. Then do the one where she sends you to minefield. Just watch out for the crazy sniper guy. He will take potshots at you the entire time you're there, plus he has this annoying habit of shooting the cars which will then explode. Anyways the place has tons of mines which you can disarm and then sell or use for the next quest at Super Duper Mart. Make sure to explore the houses completely, there are a few prewar books in them.
Eventually Moira will send you to Arlington library. You have those prewar books right? Because there you will meet a Brotherhood of Steel scribe who will buy them off you for 70-100 caps a piece.
And there you go if you do this you should have a base of operations and a nice stash of loot. To learn how to use power armor just continue doing the main quest, eventually you'll reach a point where you can learn it. If you bought the game of the year addition do the Point Look Out dlc first. The enemies there are really tough to beat at later levels. Exploration is the name of the game in Fallout 3, so explore every location you come across, you'll never know what you might find. Be sure to check out the Fallout Nexus if you bought the PC version, there are some awesome mods.
