Hello!
There are two way that you. can transfer files between your Macs. The first is transfer the files to an external flash drive or hard drive then transfer back to the new Mac. The second is to use. one of Apples built in tools, Migration assistant, to help you transfer the files. I personally recommend using migration assistant. I will provide link for both process below but be aware that the manual process article is not being updated by Apple anymore.
How to move your content to a new Mac: https://support.apple.com/en-us/HT204350
OS X: Manually migrating data from another Mac: https://support.apple.com/en-us/HT202910
Let me know if this helps!