Let's say file1.txt contain the following text.

Line 1
Line 2
Line 3
Line 4
Line 5

The following sed statement can be used to print the every line in file1.txt that contains "Line 1". Typically, you would use grep for this kind of filtering.

~]# sed -n '/Line 1/ p' file1.txt
Line 1

The following sed statement can be used to print the text between Line 2 and Line 4.

~]# sed -n '/Line 2/, /Line 4/ p' file1.txt
Line 2
Line 3
Line 4

The following sed statement can be used to delete the text between Line 2 and Line 4.

~]# sed -i '/Line 1/, /Line 3/ d' file1.txt
Line 1
Line 5