Don't lose hope!
Code formatting can be a tricky thing, and it can take time and patience to discover mistakes.
1. You're right about this one, when you don't close just one tag, it can upset the format of your entire passage. If you see this is happening, like in your example, make sure that for each tag you've added a close for it. If necessary, you can use the "Remove Formatting" button, which will remove all tags, and start over.
2. Save often. One of the easiest ways is to highlight all the text, right click, and "copy." This way you'll have "stored" the entry, allowing you to paste it back into the dialogue box if it gets accidentally erased. You can also try practicing your post with formatting HERE
, which works much like the "Preview" button here on Elliquiy does.