Usage:

tail file ...

Print the last 10 lines of each file to standard output.
With more than one file, precede each with a header giving the file name.
With no file, or when file is -, read standard input.

• $ tail -f file1

  $ tail -n 50 file1

The following options can be used:

-c, --bytes=[+]NUM                output the last NUM bytes; or use -c +NUM to output starting with byte NUM of each file
-f, --follow[={name|descriptor}]  output appended data as the file grows; an absent option argument means 'descriptor'
-F                                same as --follow=name --retry
-n, --lines=[+]NUM                output the last NUM lines, instead of the last 10; or use -n +NUM to output starting with line NUM
    --max-unchanged-stats=N       with --follow=name, reopen a FILE which has not changed size after N (default 5) iterations to see if it has been unlinked or renamed
                                  (this is the usual case of rotated log files);
                                  with inotify, this option is rarely useful
    --pid=PID                     with -f, terminate after process ID, PID dies
-q, --quiet, --silent             never output headers giving file names
    --retry                       keep trying to open a file if it is inaccessible
-s, --sleep-interval=N            with -f, sleep for approximately N seconds (default 1.0) between iterations;
                                  with inotify and --pid=P, check process P at least once every N seconds
-v, --verbose                     always output headers giving file names
-z, --zero-terminated             line delimiter is NUL, not newline
    --help                        display this help and exit
    --version                     output version information and exit

NUM may have a multiplier suffix:
b 512
kB 1000
K 1024
MB 1000*1000
M 1024*1024
GB 1000*1000*1000
G 1024*1024*1024
and so on for T, P, E, Z, Y.

With --follow (-f), tail defaults to following the file descriptor, which means that even if a tail'ed file is renamed, tail will continue to track its end.
This default behavior is not desirable when you really want to track the actual name of the file, not the file descriptor (e.g., log rotation).
Use --follow=name in that case.
That causes tail to track the named file in a way that accommodates renaming, removal and creation.