First you will need remote access software, such as one of the recommendations above. Once you have completed the setup on both the controlling computer and the remote computer you wish to access, it's as simple as selecting the computer you wish to remotely log into and then hitting connect. Some remote desktop software such as Chrome Remote Desktop utilize an application on your mobile device that you open and select the remote desktop you wish to connect to via an internet connection. Others, such as TeamViewer require you to install remote access software on the computer you wish to connect to and work via their program. Either way, you will be required to gain permission and most likely enter a password in order to log in to the remote access desktop.