making a sentence bold, or underlined

Thanks for the reply - "Mozilla Support how do i make a sentence boldface Zenos Oct 29, 2017, 3:40:41 AM You need this formatting toolbar. You'll only see that if you are composing using HTML formatting. Note that I have placed the cursor on the Bold button to show you its tooltip. A difficulty with replies and forwards is that Thunderbird may choose to offer plain text mode, particularly when there is nothing in the original message that requires html formatting. Under some circumstances you might select all the original message and paste that into a new blank html formatted message. Thunderbird sets up html formatting as the default when you install from scratch. You can set and unset this in account settings. See the second picture. There are add-ons that can help out by asserting html mode always, and not just as appropriate." I don't see any pictures, so your reply is a little too "techie" for me. Please try a simpler approach. Thanks!