Assuming you're using the CLI tools (since the machine should be up all or most of the time), you should start the daemon process `monerod` with the `--rpc-bind-ip` option, and then the IP address of the machine, e.g.:

	$ monerod --rpc-bind-ip 192.168.0.100 --detach

Then any other device on the same `192.168.0.*` network will be able to point to your internal node, e.g.:

	$ monero-wallet-cli --daemon-host 192.168.0.100 --wallet-file ...

If you're not using the CLI tools, but the Monero Wallet GUI instead, you can still pass that `--rpc-bind-ip` option on the **Settings** page in the "Daemon startup flags" field. Equally, from other machines, you can point to the remote node in the "Daemon address" field (also on the same Settings page).