If the ip address is still unknown use a computer to find the Raspberries IP address that got assigned via DHCP. The web page of the router will show the IP address.
If zeroconfig is configured then use Raspberrypi.local as <ip>
As regular user use ssh <ip address> or if working with as different user ssh <username>@<ip address>
on a computer (or putty if Windows) to access the Raspberry
When working frequently with raspberry devices the computer will detect that a different/new hardware got plugged in and becomes scared. Since this is not a cyber attack delete in the ~/.ssh/known_hosts file the keys created for the previous device and restart ssh.
If ssh is not enabled yet, insert the SDcard in a Linux computer and observe fdisk -l and then cat /etc/mtab. The SDcard will have two partitions: a FAT partition called boot and a Linux partition called rootfs.
Windows PCs will most probably struggle with such a SDcard. Enable ssh: cd /run/media/<username>/bootfs/
and create the empty ssh file in the boot partition touch ssh. Insert the SDcard, connect the Raspberry to the network and power up.