What is the meaning of "She'elunu"?
Radak: [Our captors] asked us [to sing for them]. Malbim - the custom was to sing to tell the praise of land in which they are, like we used to sing the praise and success of Yerushalayim. Now Bavel is your residence, like Yerushalayim used to be! The success that you had there, you will have here with us.
What is the meaning of "v'Soleleinu"?
Rashi citing Menachem: It refers to kinds of instruments, because they are Soleh (hang) them. They are Soleleinu (instruments) of Simchah.
Rashi: It is an expression of jesting; our enemies mocked us. This is like "Meholalai Bi Nishba'u" (102:9).
Radak #1: Rejoice with playing the harps that we were Soleh (hung) on the willows.
Radak #2: This is like Yilelaseinu; it is the same grammatical form as Toshvinenu. In place of wailing, they asked us to rejoice.