Select a clip on the timeline, then choose its Speed in the Clip settings: 0.5×, 1×, 1.5×, 2×, 4× or 8×. The same choices are in the clip's right-click Speed menu.
A note shows how long the clip plays now, such as 12.0s of recording plays in 6.0s. The clip on the timeline shows its speed too, for example 6.0s · 2×.
Voices keep their natural pitch at any speed.
To speed up only part of a clip, split it first. See Trimming and splitting.