What are Mechatzetzim?
Rashi (10): They are robbers and tax collectors who wait in ambush where people cross water.
Rashi citing Menaxchem: They are troops.
Rashi: They are loose rocks in the river. People who went to draw water feared stepping on them, lest the enemy hear. Now there is no fear.
Radak: They are archers. Before, people could not draw water due to them. Cavalry and archers made loud noises and blow Shofaros to frighten the nation - "mi'Kol Parash v'Rome Keshes Borachas Kol ha'Ir" (Yirmeyah 4:29).
Malbim: [Hashem made Sisera think that he hears] great army camps [and this caused panic amidst his camp, and their defeat].
What is the meaning of "Yesanu"?
Radak: It is learning and teaching. Targum Onkelos of v'Shinantam (Devarim 6:7) is u'Sesaninun.
Metzudas Tziyon: Speak about, like the Targum of v'Shinantam (Devarim 6:7 - u'Sesaninun) and "Lesanos l'Vas Yiftach" (below, 11:40).
What are Tzidkos Hashem?
Rashi (10): He gave serenity to Yisrael so they can dwell in open cities and go alone, without a group.
What is the meaning of "Yardu la'She'arim"?
Rashi (10): They returned to their cities. Previously, they had gone to the fortified cities.
Malbim: People had descended to the fortified cities to hide from the enemy.