If you are having trouble getting ideas flowing, then you can do what's called pre-writing. There are several methods for generating ideas. For example, freewriting (where you just write whatever comes to mind about the topic without worrying if it will be good or not), clustering (where you draw out categories and connect them to each other), having a conversation, making a list. These are all ways to start yourself along the right path to figuring out the points you want to make.
If you already have ideas, then you should move to structuring your paragraph. Start with a sentence explaining what your paragraph is about (friendship). Then move into talk about your main points.
After you've drafted a paragraph, post it in the notebook section for help from others on grammar and wording.
Good luck!