First off, welcome to a fine hobby!
As for painting, use an airbrush, and put the major assemblies together (i.e., fuselage, wings, horizontal stabs)
The decals are the water-release variety. Trim closely around the decal using small scissors, like the ones some use to trim fingernails (look in the women's cosmetics section of Wal-Mart and the like). Then, place the deals in a bowl of warm water and let them soak for about 10-15 seconds, then place the decals on the plane (after painting, of course).
Another tip on painting the landing gear: paint all the struts and wheels while they are still attached to the trees.
As for trimming the pieces off the trees, use some sprue cutters (Xuron and Testors are two good ones), a hobby knife for rough clean-up of the area where the parts were attached, then varying grades of hobby sandpaper for fine clean up (start with the rough paper, then work to the finer grades).
I am by no means an expert, so I am sure there are those out there with more and/or better ideas.
Former ZW F/A | "Wisconsin 72A, contact departure, see ya."