I just got a tube amp and I have some questions. My friend told me if I have either the volume or the master up all the way I get better distortion. Which one is it? If I have it all the way up will turning the other one up drastically increase the volume without turning it very far, possibly blowing the speaker? What happens if I do the opposite of whatever gets the better distortion? Better clean tone?
What amp is it?
Your friend is referring to power amp distortion over preamp distortion. Cranking the master will give power amp distortion which gives a more classic sound like AC/DC, plexis etc (not exactly like that but you get the picture) while preamp distortion generally gives you a more modern distortion sound.
Theres no better really it depends on the sound you're after.
Gain increases the overdrive/distortion. On pedals theres sometimes nobs that say dist. or od. They increase they ammount and the gain increases the power.
like a classic rock sound? find a mix.

for a heavier sound, master lower, volume higher or maxed. also, if your amp hasa mid boost, take it OFF!!!!! the difference is amazing. not so much teaking the EQ but un-boosting the mids makes your tone + distortion immediately heavier.

for example i have a bugera 22 watt. if i want a heavier sound- master down, volume up, bridge pickup tone on like 3, click on my boss distortion and turn off mid boost.

i can leave the mid boost on and rock the boss, but its not as deep. unclicking the mid boost is a whole nother sound.

on the other hand with my setup teh midboost really helps with a classic/hard rock sound.