1) Put depot, expand it if you need, change the name of the depot station. You also need to change the combinator signal (it works like filter) from iron ore (or crude oil for fluid depots) to the resourse you need. Change the train path to use the proper stations and copy it to other trains in this depot. 2) Put some provider (load) and requester (unload) stations. Be sure they connected to the circuit network by big power pole. Set request signal. Change the name of the stations. 3) Done!