Thanks
But if they are changing addresses each time for security is it best not to store an old address to use when I am not near my Ledger Nano?
I'm quite new to all this

They're
not changing the addresses for security, but for anonymity changing the addresses for both security AND anonymity. It just makes it harder for people to track how much bitcoin you have, using a block explorer like the blockchain.info[1] explorer. Should you re-use an old address? That's completely up to you. Remember: The bitcoin blockchain is public. So if a certain person knows your wallet address, he/she can look it up online to see how much bitcoin that wallet is holding.
[1]
https://blockchain.infoEDIT: Thanks Lauda for correcting