Magical bytes are four bytes that signifies the start of a new message send by a node on bitcoin network. The messages gotten on a bitcoin network by nodes are usually a continuous generated data so this magic bytes are actually the separators of each message. In a simple language they’re like maybe a comma or full stop to each message. Read here
learnmeabitcoin.com.
And if I wanted to use it, what would I need to do in bitcoin technology to use magic byte?
This knowledge will be useful if only you would like to run a bitcoin node.
Is it When holding bitcoin in a non-custodian wallet or for transactions, is it necessary?.
Nahh this has nothing to do with holding your bitcoin in any wallet. Just like the link started above there is nothing extraordinary about it rather than differentiating/separating two messages on the bitcoin node