Installing Linux on external drive. Erase disk installation vs manual partitioning

Running Distro live & then Installing it on external drive is not something very difficult but the main issue is partitioning. I don't know partitioning, tho many Linux distributions like Ubuntu provide erase disk installation, it erases the full disk & then maybe automatically configures all the partitions on the drive & then installs the OS completely on the external drive

Anyways most of the distros do not provide that second option which automates the full instalation process instead they provide manual partitioning option. What I want to know is how do I install a Linux distro which only has manual partitioning as an option? i have zero idea of manual partitioning

Also which option would be better for installing Ubuntu or any other distro on External SSD Erase disk installation or manual partitioning? Which one would be good performance wise or will it even effect the OS performance at first place?