The electrical code stated that two # 10 wires can be pulled into a half inch conduit.
It varies by conduit type. If you don't know the type, use 9.
There are both industrial and home owner cable pulling techniques. The former may involve heavy equipment and cable greasing and many people. Pulling cable on a small scale involves a snake and sometimes a pull cord. A snake is a coiled metal strip that you push through the conduit. When it comes out the other end or to a pull box you connect the wire and pull it back through the conduit. If more wire might be pulled later, also attach a pull cord so it will be left behind in the conduit for future use.
Need to know the wire # size to compute wire fill in conduits