Let's start make this simple since you don't seem to have a grasp of even the most basic principles.
A public pool is a collection of individuals who "pool" their mining equipment and mine BTC together. They share the rewards once a BTC block is solved by the pool. The rewards are in proportion to your hashrate... members of the pool with higher hashrate receive a larger share of the rewards. The reason people mine in a pool is because it reduces risk. It is incredibly difficult to solo mine a block unless you have a massive mining farm.
Here is a chart which show the hashrate distribution of public and private pools...
https://blockchain.info/poolsYou'll probably want to join a larger pool especially if your rental contract is for a short time. That is not a popular choice amongst home miners. They would rather you chose to mine on a smaller pool to support decentralization. But mining on a small pool can be risky since you may mine for days and not find a block and your investment will have gone to waste. A solid mid-sized pool might be your best choice.
Below is a list of pools that I've used...
Large pools (Chinese)
- F2pool/Discus fish
https://www.f2pool.com- Antpool
https://www.antpool.com/home.htmMedium pools
- Eligius
http://eligius.st/~gateway/- Slush's Pool
https://mining.bitcoin.cz/home/Small pools
- Kano CKPool
https://www.kano.is- Bitminter
https://bitminter.comThere are other pools that I have not tried like BW.com. And there are private pools that are not open to the general public like Bitfury and KNCminer.
Once you join a pool, you'll need to find the URL to enter into your miner settings. This will be unique to each pool. It will look like this...
stratum.kano.is:3333
stratum.antpool.com:3333
Next you will need to register a unique username and workername with the pool. Sometimes the workername will be automatically detected by the pool so you don't need to choose one in that case. It will look like this...
username_workername
or
username.workername (Some pools will accept both "_" ".", other pools might require one or the other.)
Obviously "username" and "workername" are just generic names. Change them.
Next is password which can usually be anything and is not important for security reasons. Most people just enter something like xxx or 123.
Finally you will need to register a BTC address with the pool to send your earnings to. So you will need a BTC wallet... which is a completely separate topic. It's not as easy as you think especially if this is your first time, lol. Some pools (like Eligius) use your BTC address as your username. But quickly... NEVER send your earning directly to an online wallet. Use a secure wallet on your computer. And be sure to BACKUP that wallet and NEVER forget your password. If you lose your wallet without a backup (hard drive crash) or forget your password, your BTCs are gone forever!
The main reason why you rental company is asking for 3 pools is for "failover". The first pool is your main pool. If that pool goes down for maintenance or is a victim of a dos attack, your backup pool will continue to mine.
Hope this helps!
