Once you've settled on the model helicopter of your choice and purchased it, you're going to have some assembly to do before you are ready to fly. The amount of assembly will vary according to the particular model and type. The degree of difficulty can also range from the extremely difficult to reasonably simple, but there are some common things that should be understood, and tools to have for the building of your model helicopter.
In the world of remote control aircraft there are terms and acronyms for different tools, parts and to describe ideas or actions. It would be wise to at least become familiar with these terms. There may be instances where you will need to describe something to a lobbyist either on the phone, internet, or in person. It will also help in understanding and following the directions in the kit you have purchased.
Before starting to build your model helicopter read the directions in the kit carefully, then re-read them. The more familiar you are with these instructions you are the less likely there will be any surprises or problems. If there are any directions that you don't understand, you can ask questions, and receive answers, that you understand before arriving at the particular step in the modeling process.
You should also note any additional materials, or special tools required and get them. Some kits require the servos and engine to be purchased separately, and these should be installed as the model helicopter is built. Also some hobbyist find several tools helpful, you should get these together: hobby vise, screwdrivers, wrenches to fit both the kit and the engine components, masking tape, modeling glue, rubber bands, toothpicks, needle nose pliers (the smallest you can find), pitch gauge, ball pliers and blade balancer. This is by no means a complete list, but it will give you a good start.
As you build your model helicopter you may want to paint the cockpit, tail, or other assemblies. One method often used in modeling is to "mock-up" assemblies. This is where parts are fitted together, but not fastened, and checked for proper alignment, operation, etc. Painting is often done during the mock-up process. Also, during the building process you may want to install any upgrades you may have purchased. In some cases simple mechanical alteration instructions are available on the internet that may be done to improve performance and handling, so do some research and ask questions first.
The most important rule to follow in the entire process is to take you time and not be afraid to ask questions. When you take your time your results will be much more satisfying, and your knowledge of the mechanical operation of the model helicopter you have assembled will assist you when you are learning to fly your new machine.