rename a word/variable - :s/target/new_value
Ex.: :s/rain/sun
rename all the occurrences - :%s/target/new_value/g
% denotes that the substitution should be applied to the entire file.
s stands for substitute.
target is the pattern you want to search for.
new_value is the replacement text.
g at the end stands for global, which means replace all occurrences on each line. If you omit g, only the first occurrence on each line is replaced.
Vy - copy the hole line (yy work as well)
Vx - cut the hole line
=ap - format file
vap - highlight the entire block of code