Like Steve said, rockets described as RTF are Ready to Fly (you might have to tie on the parachute, but they are pretty much ready). Rockets that are E2X are Easy to Assemble (X-semble?), which means you will have to glue some parts together, but you won’t need to paint the rocket. You can have one of those ready to go in a few hours, and give it a day for the glue to cure. From there, they go up in the amount of work and skill required, and most kits are labeled with Skill Level 1, or 2 or 3, etc. These kinds of kits are just parts — tubes, fins, nose ones, centering rings, motor mount tubes, parachutes, etc. You need to measure and mark the tubes, glue things together in the right way, paint the rocket, etc. You may need to cut a few things or sand some parts. It’s easy to learn, but it takes some time and effort. Some people really enjoy the building process.