When you reach a higher reputation level (or amount of Steem Power) - I am not sure which. You will then see a slider that allows you to adjust your vote from 1%-100%. If you vote at 100% you have 10 votes per day as it keeps topping itself up. You should be able to find some good articles about it - just click the search button (magnifying glass) at the top of the page and do a search. Try to find more recent articles.
You can check your voting power here https://steemnow.com - enter your username in the top right corner. I hope this helps.
Edit: Just saw this article which will explain a bit more - https://steemit.com/steemit/@calamus056/how-to-improve-your-curation-quality
Thanks! There is so much to learn!