You can build roads on any land you want by selecting the set/eng and hitting the R key. You will see an "R" on his shield while he is working, which disappears when the road is done. For irrigation you need to be on or adjacent to a water source (ocean, lake, or river) OR full-bordering (not catty-cornered) another tile that has already been irrigated. Select the set/eng and hit the I key, and an "I" will appear on the shield till done. Some tiles cannot be irrigated (Mountains and Glaciers), or irrigation converts them to other things (like Swamp turns to Grass). For Railroads you need the Railroad advance, then you need to have a road on the tile already. Automating a set/eng with the K command is not a great idea, because the computer will take over control and decide on strange orders of doing things. Better to keep them under your own control.
