Nu-Nu the eel said:
Nope not easy to do. Might want to do some research.
+1. When Nu-Nu says do research, trust me...he is 110% right! He has successfully kept fish and corals so any advice he can give would be worth listening to!!!
In my opinion, you should consider a bigger tank (at least 20-30 gallon). While you are saving in cost for the 10 gallon you will probably be doing maintenance every other day to every few days if you want to keep algae and other gunk out. In addition, you probably could keep two fish (very small) and thats it in a 10 gallon. Planning, preparing, and patience are the keys here.
Here are some things you can do to start planning:
1. Look up the fish you think you might want. They have minimum space requirements. If these aren't met they will most likely get stressed and die. Liveaquaria.com can give you some basic info on fish. Make sure when you get a fish that it will be compatible with the others you want. Will you ever want a reef? Consider that when buying fish and equipment. It will save you money.
2. Look up "nitrogen cycle" and read it a few times. If you can't get this out of the way and finished you will never be able to keep fish without killing them. This is how you get the bacteria that breaks down waste in the tank. Here's a good reading start:
www.fishlore.com/NitrogenCycle.htm
3. Prepare to spend some money. I believe that prevention is better than digging for solutions. Most marine hobbyists use RO or RO/DI water. If you do this now that's great. You will need a decent filtration system etc. Again, here is a list to start with however do research because I assure you we all have different things in addition to meet our needs. Sit down and make a list of items you need, items you want, etc. and list the prices. There is quite a difference in cost for freshwater vs. saltwater. We aren't trying to discourage you however it's important you know all this before leaping in.
www.fishlore.com/SaltwaterAquariumSetup.htm