Ubuntu 18.04 Backup to External Drive Partition

I have a Ubuntu 18.04 on my system which has 200GB/256GB is used. I bought a external hard drive with 1 GB storage. I don’t want to use it all for backup. Is it possible to partition the externl harddrive 256GB to backup and the rest to use for other data like a USB stick drive ?

How do I configure Backups app for this purpose to store the backups on that partition only in the hard drive? Also I want that partition on hard drive to be non visible to other PCs is that possible ?