You can remotely gain access to the command line of a Raspberry Pi from another computer on the same network using ssh.
Note you only have access to the command line, not the full desktop environment. For full remote desktop see VNC.
You can enable or disable the SSH server on your Raspberry Pi (it is enabled by default). This is done using raspi-config:
Enter sudo raspi-config in the terminal, then navigate to ssh, hit Enter and select Enable or disable ssh server.
SSH is built into Linux distributions and Mac OS, and a third-party SSH client is available for Windows. See the following guides for using SSH depending on the operating system used by the computer you are connecting from: