When you look at a vendor like Zavala or the faction leader you should see a number above the progress bar on the right side. That number tells you what rank you are. Generally it takes 20 tokens to level up so if you want to reach rank 50 you need 1000 tokens. Zavala - Tokens are obtained from completing strikes and daily strike challenges. Faction - Public events, strikes, lost sectors, enemy supplies, certain scannables, weekly faction challenges (on each character) and crucible give tokens. Tokens vary per event and amount of renown you have.