Do a Google search on building AK's. There are sites that have excellent instructions and sell the special tools needed.
Building an AK is nothing like building a modular rifle like the AR-15.
You need special tools, including a large shop press, usually a spot welder, a special riveting tool, and other specialized tools.
Back in the days when AK kits were cheap, you could save money by building your own rifle, and there were AK "build parties" where a number of people would all gather at someone's house and use his tools to assemble their rifles with help from the others.
Now that kits are hard to get, expensive, and don't have the original barrels included, you're really better off just buying a rifle, especially if you intend to only build one or two rifles.