If in any doubt, you can see by looking at this picture - that will tell you if any tags (Which is what the commands between the [ ] sign are called) is open.

To ensure that the
Bold can work, click on CLOSE ALL TAGS - As seen next to the COLOR.
This will make sure the correct command is given and give the command to close the bold.
The close tag looks something like this: [/B]
A close tag is like the one you have started the command with, but with a forward slash in there between the [ and either letter or wording you use.
So for example a closed tag for Italic would look like this: [/I] or [/i]