This assumes you have a NFS Share setup up. If you do not you can follow this link.
Open up XenCenter click on add storage device button on the top.
Select NFS iso and hit next.
Enter in the name you want to call your repository
Next we add the share location which in my case is 192.168.200.250:/nfs and hit Finish.
If all went well you should have a new NFS ISO repository
This assumes you are connected to your XenServer with XenCenter. First you need to mount the xs-tools.iso on the system. To do this right click on the VM you want to install XenServer Tools on and click “Install XenServer Tools”
Then from the console tab do the following as the root user, or just type sudo before each command
mount /dev/cdrom /mnt/xs-tools
After it finishes, you need to reboot.