If bidding starts at $10 then the first bid will be for $10. So lets assume someone has already bif 10, then the next bid will probably be $11, then 12 etc. If you put in a bid of $50 you will be shown as the highest bidder at $11. If I bid then I will be told I have to bid at least $12. Say I do bid $12, I will then be told after my bid is placed that I have been outbid, and the highest bid is now $13, and I need to bid at least $14. So I bid 14 and am told again I have been outbid and the item is now at $15 - with you still as the highest bidder. That will go on until the item gets up to your bid limit of $50.
So if no one bids $51, you have won the item. Not sure if this is still the case but at one time you could set the bid amount. ie if you were entering an item for auction, you could set the start bid at $10 and bids must be in the minimum of $5 per bid, so the item would go up in 5s.
So if you want the item and you won't be able to be watching the auction end then you are safe in bidding your limit of $50 when you are online. However there is some software available that will snipe the item in the last 30 seconds of the auction, ie outbid you without leaving you time to counter bid. This stuff is very clever and ideal if you want to win auctions.
My preference is not to bid at all, but to click on the item and tell ebay you want to "Watch" the item. Ebay will then remind you near to the auction ending, giving you time to log in and bid for the item if you wish. I find that if someone has pre bid up to say $50 and I decide to bid on the item, it encourages me to bid up to my limit to see if I can win. So if I want to bid $30 for your toy, then I will cut out at $30 leaving you as top bidder at $31. However if you had not bid, I may have just bid $11 and left the item until nearer the end time, when as I watched thinking I am winning the item, you can come in with just seconds to go and bid say $23, just to make sure you cover any pre bid I may have put in, and you will win it at just $12, a much better result for you.
So you pays your money and you takes your pick.