When you add vocal to backing track, when you have finished and want to clean it up, i.e compression, EQ etc do you just high light your vocal track and edit, or do you include your backing track and make the same changes to both. Thanks
That’s up to you!
When you say “clean it up”, that implies that there’s something wrong that you want to fix. 
With a “pro” multi-track recording, the 1st step would be to get the best quality to start with.
Then, during mixing, you’d adjust the volume & panning of the individual tracks, as well as add effects to the individual tracks. Different tracks will generally get different treatment depending on what you are trying to accomplish. Compression is probably the most common effect, used on almost everything. EQ is common too, but with a good mic you shouldn’t need a lot of EQ, and you may not need any. (It is very common to filter-out the deep bass from everything except the bass guitar and kick drum.)
There usually be certain effects added to the overall mix too. For example, you might want to apply reverb to the mixed tracks so all of the vocals & instruments get the same treatment and it sounds like they were all recorded in the same room together.
Then after rendering, the final mix would go to mastering where a “different set of ears” is used for any “final touches”. Typically this will include level adjustments and compression/limiting, and maybe a touch or EQ and/or reverb.
Some classical or acoustic recordings are made in concert halls or “good rooms” and no artificial effects are used at all! But in most cases there is at least some compression/limiting to bring-up the overall volume and to limit the dynamic range for “casual listening” where you don’t want dramatically quiet or dramatically loud parts.
P.S.
The most important thing to know when mixing is that mixing is done by addition. If you are mixing two tracks, keep the levels of each track below 0.5. If the mixed tracks go over 100%, you’ll get clipping (distortion) when you render to a “regular” WAV file or if you play the file full-volume into your digital-to-analog converter, etc.
If the mix doesn’t sound loud enough, you can normalize the final mixed file (or use some dynamic compression).
Thanks for all that info, I bought a backing track and just recorded me singing along to it. came out ok but was playing around to see if I could improve the sound. One more question, i have a church sermon recording with alot of echo, what noise gate do i need to download for windows xp and is it straight forward to remove the echo effect. thanks again.
There is a Noise Gate here http://wiki.audacityteam.org/wiki/Nyquist_Effect_Plugins#Noise_Gate.
Installation instructions: http://wiki.audacityteam.org/wiki/Download_Nyquist_Plugins#install .
It is extremely hard to remove echo. The Noise Gate will only reduce or silence echo between the words of the sermon.
Occasionally you can use Noise Removal to select some echo as Noise Profile then ameliorate the echo that way. That may sound worse than doing nothing.
Please be careful with XP. It is a security risk given Microsoft no longer supports XP with patches. See https://forum.audacityteam.org/t/audacity-not-saving/35590/3
Gale