Welcome to fishkeeping, and welcome to TFK!
I wanted to add to be sure to get your larger tank exactly level. It doesn't really matter with very small tanks like a 10g, but with a larger tank you will want to be sure to get it perfectly level to avoid future issues with stressing and leaks.
And, to just clarify some previously mentioned things-
Research how to do a "fishless" cycle. It is cruel to use fish for a "fish-in" cycle, and there are quick and easy ways to cycle without harming fish. You can start by reading here http://www.tropicalfishkeeping.com/f...quarium-74891/
and here http://www.tropicalfishkeeping.com/f...m-cycle-38617/
And on planted tanks here http://www.tropicalfishkeeping.com/a...um-part-34861/
(You'll see that adding water from an established tank will do nothing, but "seeding" with biomedia from a HEALTHY established tank (filter media, substrate, decor, plants) will be very helpful.)
You'll need to purchase a API Master Kit, which is a liquid testing kit that will inform you of your tank's pH, Ammonia, Nitrite, and Nitrate. These are values you MUST have when cycling your tank and being a new fishkeeper. Test strips are notoriously innaccurate, pretty worthless. Pet stores may test for free, but they often use test strips or give you readings like "okay" or "normal". You'll need to know the exact values, the convenience of testing your water at home, and the accuracy of a liquid test kit.
While you're cycling your tank, you can decide on which fish you'd like to have. You can look up the fish and plant profiles at the top of the page labeled "Tropical Fish Profiles" in the dark blue navigation bar. The rest of the tank (plants, lights, decor, filtration, etc) should be set up around the needs of the fish. You can post questions here at each stage and we can guide you through the innumerable choices out there.
Please note that having female livebearers can lead to hundreds
of babies within a short month or two. Females can even store sperm for months after having been removed from a male! All the babies are cute at first... until you're out buying a bazillion new tanks for all the babies, not being able to find homes for them, being turned down by stores that may have said that they'd take the babies back, etc. Its really insane how quickly you can get buried under a mound of livebearer fry! So first rule of fishkeeping- research, research, research! And we're here to do whatever we can to help! Good luck!