With hover reading, you point at text with the mouse and, after a short pause, Readable speaks it. Choose how much you hear from the Hover ▾ dropdown on the toolbar:

Hover dropdown listing Hover off, Word hover (ticked), Line hover, Sentence hover, Document hover and Text extractor (OCR).
The Hover dropdown. The tick shows the current mode — Word hover by default. Ambient sound also appears here once you choose a sound in Settings.
Hover off
Hover reading is switched off.
Word hover
Reads the single word under the pointer. This is the default.
Line hover
Reads the whole line the pointer is on.
Sentence hover
Reads the whole sentence, even when it runs across several lines.
Document hover
Reads everything in the window from the pointer downwards — see below.

Video help

A short video showing this feature in Readable for Mac v2. The video only contacts Vimeo once you press play.

Hearing words, lines, sentences or passages by pointing at text

Holding Control or Option to hover

By default, hover reading only speaks while you hold down ⌃ Control or ⌥ Option. This stops Readable talking every time the mouse passes over text. To have hover speak without holding a key, open Settings, go to the Reading tab and untick Require Ctrl/Option for hover-speak.

Reading tab of Settings with Require Ctrl/Option for hover-speak ticked, Speak when text is selected unticked, Speak text captured by Text extractor ticked, and the underline options.
Settings → Reading, with the default settings.

Document hover

Choose Document hover and point at the place you want to start. Readable reads from the pointer down to the bottom of the window, including text in PDFs, images and apps that don’t share their text. The whole width of the window is captured, so nothing at the edges is missed, and multi-column layouts are detected so only the column you’re pointing at is read. Press Esc or click Stop to halt.