If you have an error, use it at search keys. Otherwise try searching with keys describing the behavior encountered.
Also you’ll probably find more results in English.
Also there are generally places in which you are likely to find results, like Arch wiki, Manjaro wiki, and this very forum. The archived forum may also provide some answers.
fstab is a file for configuring how to mount defined partitions. gnome-disk-utility (Disks) can serve as a frontend for it.
Otherwise you can also use systemd.
Reinstallation – from the same liveUSB indeed – usually involves scratching the previous root partition. So if you did not make a separate partition for your data beforehand, that will be indeed lost. Unless you save it on a spare drive before reinstalling.