Examples

White can open the back-rank by exchanging queens with Qxe5.
Black has to recapture with the rook, which is deflected from protecting the now open back-rank.
White can then exploit the weak back-rank with Rd8+, forking king and bishop.

Black can open the line from g5 to g1 with the knight sacrifice 1...Nh3+!
White cannot play Kh1, because Nxf2+ would be devastating.
White therefore has to capture the knight with 2.gxh3, opening the g-file.
Black can then win the rook on d2 with the queen fork 2...Qg5+.

Note that Black has to capture the rook with the Queen to avoid a counter tactic.
For example 3.Kh1 Qxd2 wins, but not 3...Rxd2? 4.Ne4 with a counter fork.
Or White could try 3.Ng4 when 3...Qxd2 wins, but not 3...Rxd2? 4.h4 Qf4 5.Re4, and the queen can no longer defend the rook.
Also 3.Ng4 Bxg4 does not work because of 4.Rg2, with a pin.

Related motifs

A line can also be opened for the fork move (instead of for the fork attack).
It is also possible to open a line for checkmate attack.