When you are voting you’re always doing it with 100% until you reach 500 Steem Power. Every 100% vote drains your overall voting power by 2% but it will refill again slowly (20% every 24 hours).
This means you can make every day 10 votes until you have reacharged again completely.
With the slider you can adjust to not vote every time with your full power. You can set it individually from 1 to 100%. A 10% vote for example will then only drain your overall voting power by 0.2%.
I hoped this answer helped you out. I wish you a lot of fun and success on this platform. If you have any further questions don’t mind to ask. I’m always willing to help :)