I recently set up an ethereum mining machine, and it was quite an interesting experience. I'd like to outline on a high level here exactly what you need to know and how set it up.
First of all, to set up a mining machine, you are going to need the hardware for it. Compared to Bitcoin, Ethereum is mined using GPUs (graphic cards basically), and not on dedicated hardware, and also not on normal computers. So you are going to need to purchase specialised hardware (the GPUs) to mine Ethereum.
Right now, there are about four GPU types that make sense in mining - AMD 570 series, AMD 580 series, NVidia 1070 series. As a second choice, you can go for AMD RX480, AMD RX470, Nvidia 1060. These are the actual graphic card chips inside the card, the model of the card may differ (e.g MSI RX580, XFX RX580 etc).
Once you have chosen your GPU, you need to purchase it online (and this is the hard part because they are all pretty much sold out now). If you find them, try not to send more than $400 on a single one, as it will otherwise lose you money.
Once you have purchased your cards, you will need to buy the other parts of the computer that you need to connect these GPUs to. These are the motherboard, processor, hard drive, ram and power supplies. You will also need some devices called Risers that basically allow you to connect your GPUs to the mainboard using USB.
Once you have all the parts together, you assemble them into an open air computer with the GPUs connected to it. Note that each mainboard can take between 6 and 10 GPUs (maybe some can take more, but at most 2 more), so for each set of cards, you will need a new mainboard to add them.
Once hardware is working, you install windows or ubuntu, then download the software that will do the actual mining. There are various options, but a good one is called Claymore - it will do everything for you - you just need to configure it with your address and join a mining pool. You typically want to mine on a mining pool, which is basically just a bunch of people deciding to pool their computers together to mine together (and share the rewards).
Once everything is working, what people typically do then is to overclock their cards. Out of the box, the GPUs will give you about 20MH/s (mega-hash per second). The megahash represents how much Ether you can mine - the more it is, the more you can mine. 100Mh/ should give you about $300/month (at current prices).
So with overclocking, you can basically increase each GPU from 20MH/s to about 30MH/s. This gives you more money for the same mining effort.
To overclock, you typically go to the GPU and modify the bios so that the memory of the card runs faster. You also modify the processor clocks of the GPU so that they run faster - you can also set it that the card uses less power. Note that GPUs have all these settings available for users to modify using a bios editor, but they can make the card instable, so you would typically want to experiment a bit to get the right settings.
There are a lot of details I have left out, but the above is basically the high level overview of how to setup an Ethereum mining machine. In subsequent posts, I will go into the details of how each part happens.