:h marks or Using marks for detailed info.
Type of marks
a ~ z: valid within one file, erased when file closed;
A ~ Z: valid between files, you can use these marks jump between files;
0 ~ 9: reserved for vi use;
Frequently used actions
(use "a" as mark name)
set marks: ma
jump to marks(line and column): `a
junp to marks(line head): 'a
list all marks: :marks
delete all marks: :delm!