this line is in italics
line 6
line 7
line 8

Our objective is to know how to post this in GW so that it turns out as above and not like this...

this line is bold line 2 line 3 line 4 this line is in italics line 6 line 7 line 8

Now, in order to see how this works, you will need to either view the page source and look at the code, or have a look at this little text file here.

Once you're looking at either the code or the text file, you will see that the strong tag is opened before the words you want to make bold and closed after the last bold word. The same happens with the opening em and closing /em tags.
Closing tags always have a forward slash in them, opening tags do not.
Tags are always surrounded by less-than and greater-than.

The line break - br / - and paragraph break - p / - tags used above are self-closing, so you just need to put one or the other at the end of the line. One "p" is the same as 2 "br"s.