Delete first character

sed -r 's/^.{1}//'

Delete first two characters

sed -r 's/^.{2}//'

Delete last character

sed 's/.$//'

Delete numbers

sed 's/[0-9]*//g

Delete empty lines

sed '/^$/d'

Transform URL in FQDN

sed 's/https\?:\/\///'

Print every lines matching $1

sed '/'$1'/!d'

Basic substitution - replace toto with tata

sed 's/toto/tata/g' file.txt

Deleting lines with multiples patterns

sed -e '/pattern1/d ; /pattern2/d ; /pattern3/d ; /pattern4/d'

Print lines who matching simple/multiples patterns

sed -nr '/pattern1|pattern2/p'

Delete first 65 lines

sed -i '1,65d' files.txt

Remove first char line only if it's a comma

sed 's/^,//'

Uncomment line that contains a specific pattern

sed -e '/^#.*MYPATTERN/s/^#//' file.txt

Extract substring between two patterns

sed -e 's/MyPattern1\(.*\)MyPattern2/\1/'

(not sed) add pattern at the beginning of each line

awk '{print "http://" $0}'

To be continued ...