If you're mining to gather ether for financial gain or to use it to execute contracts on the main net, that's not the way you do it.
You got the ethminer part right. You just don't need geth unless you're trying solo mining, but that's not profitable anymore.
If you want to mine ether, the first thing you'll need is an ethereum wallet. You can get one on https://www.myetherwallet.com/ (please, ALWAYS double-check links) or an exchange (like coinbase, bittrex etc).
You'll need to mine against a mining pool, which is the best way (if not the only one) to mine widely spread coins like ether. In a nutshell, you 'sell' hashpower to a mining pool and they give you ether in return. Shares calculations varies among pools, so you'd have to check the one that best suits your needs.
Usually, there are instructions on how to set up your miner on mining pools websites. To mine against Dwarfpool (which I use), the easier way to just start mining is:
ethminer.exe -G -F http://eth-eu.dwarfpool.com:80/YOUR_WALLET
Please bear in mind that CPU mining is not profitable for ether. You'll need a GPU with at least 2GB RAM (4GB is good, 8GB is great), so the -G flag above tells ethminer to use GPU. You need to replace 'YOUR_WALLET' with your actual wallet address. You can check ethminer options by running:
There are several additional details to improve performance etc, but I think these are the basic instructions to get you up and running.