how to establish sql server express remote and local connections among three pcs , networking sql server

I have three systems, Sql Server Express only on one. I would access sql server on main pc from the other two to enter data into a database using a winform application. all three pcs are on LAN. what do i have to do establi开发者_如何转开发sh connection with sql server on the main pc from the other two pcs? That is, how do i network my sql server express so that it is installed only on one machine but used by two other machines also. What protocols would i have to turn on or off? All 3 pcs are in a same room. Also, sql remote connection means connecting via internet?