Although you can visit a plot rented by another player, you have no right to mine or build on that plot. You cannot take anything from that plots storage unless you have already bought those goods. If anything is for sale on the plot, you may purchase what you need. Also, if the owner of the land parcel is looking to hire any workers, any jobs available, will be posted there. If you press the button "Free plots", then you will separately sorted free and separately rented plots.
If this plot is occupied by anyone, you will see the "Info" tab on it or you can use the filter and select all occupied areas.