due to redhat regulations.I can not put external links here.but I can tell you sources where u can get free books about Linux.search pdfdrive in google.It is a free website offer free books to download.sander van vugt Linux books are good for starters like you.Hope this help you.below are some Linux book you can follow.
1.Red Hat RHCSA/RHCE 8 Cert Guide: Red Hat Enterprise Linux 8
2. Beginning the Linux Command Line
3.Beginning Ubuntu Server Administration: From Novice to Professional Sander van Vugt
all these book you can download in pdfdrive