The site begins with some basic grammar. For example, if you sometimes use the wrong form of a verb, this exercise may be useful to you: Forming Verbs: Choosing the Right Form.
If your writing is already pretty good, look further down the page and you'll find exercises to improve it even more. This is especially important if you're considering studying in the West because you'll have a lot of writing assignments. The exercises can also help with grammar for speaking.
Suggestion: If you want to use those exercises, practice every few days (or every day). It won't help you much if you only do it once.
