Gunplas (Gundam models) are generally classified into a few difficulties, and the most notable ones are HG, MG and PG, in terms of increasing difficulty.
1/xxx refers to the size of the model compared to the "actual" Gundam, so a 1/144 means that it is that the model:real size ratio is 1:144.
From the looks of the size, it should be a HG grade, which should be relatively simple, even for beginners. Just follow the diagrams, use some simple cutting tools (even nail clippers will do if you are not too "professional") and you'll do fine. Just be careful, especially with their "V fins" or those things on a Gundam's forehead. They are usually the easiest part to break.