You have three UI options for logging into your Raspberry Pi:
1. The “standard” way: connect a USB keyboard and HDMI monitor directly to the Pi.
2. connect a PC or Mac to the Pi by plugging a USB-to-serial console cable like the Adafruit 954 into the Pi’s GPIO header, and use the Terminal app on your laptop to connect and login to the Pi as described here.
3. connect your Pi to your local network and then use the SSH app on your Mac to open a remote session on the Pi as described here.
I use all three methods, and each has its benefits in different situations.
Once I’ve initially setup my Pi for networking using option 1 or 2, I find the third option – connecting via LAN – most flexible, since it doesn’t require the Pi to be tethered to my Mac or any other equipment. I can power up the Pi on my workbench, and as soon as it’s connected itself to the WiFi, I can SSH into it from anywhere in the house. Or even over the Internet if I open a port in my router for the purpose.
You sometimes need to find out the MAC address of your Raspberry Pi. For instance, you want to find it among the list of devices attached to your LAN, because you want your router’s DHCP service to assign your RPi a permanently dedicated IP address instead of letting the DHCP just assign it the next available IP address each time you start it up. Then you can SSH into the same IP address each time to log into your RPi from your PC or Mac knowing it will always be there, without having to search for the RPi on the network.
Some LANs are configured to allow access only for a white-listed devices by MAC address, so you’ll also need to know yours to be able to use such a LAN.