In act 4, scene 3, Malcolm and Macduff discuss the dire conditions of Scotland under Macbeth's tyrannical reign. After Malcolm mentions to Macduff that they should find a solitary place to weep, Macduff responds by telling Malcolm that now is the time that they should take up arms against Macbeth. Macduff proceeds to describe the terrible situation and environment in Scotland by telling Malcolm the following:

Each new morn
New widows howl, new orphans cry, new sorrows
Strike heaven on the face, that it resounds
As if it felt with Scotland and yelled out
Like syllable of dolor (4.3.4–8).

Macduff is basically telling Malcolm that each day women's husbands are dying, orphans continually cry, and even heaven feels Scotland's pain. Macduff's description of Scotland communicates the country's chaos, disorder, and suffering. Under Macbeth's tyrannical reign, the citizens of Scotland suffer immeasurable hardships, and Macduff wishes to restore Scotland to its former glory. Macduff proceeds to lament the need for a righteous king while Malcolm cleverly tests his loyalty.

These lines are spoken by Macduff at the very start of Act IV, Scene 3.  He is talking to Malcolm.  The two of them are in England where Malcolm has gone to try to get help to take Scotland back from Macbeth.

What Macduff is doing here is telling Malcolm how bad things are in Scotland.  He is telling Malcolm that Macbeth has been doing all this bad stuff.  Specifically, in these lines, he is saying that Macbeth is killing many people.  That is why there are new widows and new orphans every morning.