"We" means Paul and, though specifically writing to the Corinthian believers, includes all believers. (See: [[rc://en/ta/man/translate/figs-inclusive]])
Paul reminds the believers that though idols have no power, believers must be careful not to affect the weaker believers who might think they care about the idols. He tells believers to be careful with the liberty believers have in Christ.
Gentile worshipers would offer grain, fish, fowl, or meat, to their gods. The priest would burn a portion of it on the altar. Paul is speaking of the portion the priest would give back for the worshiper to eat or sell in the market.
"Knowledge puffs people up." Here "puffs up" is a metaphor for making someone proud. The abstract noun "knowledge" can be expressed with the verb "know." Alternate translation: "Knowledge makes people proud" or "People who think that they know a lot become proud" (See: [[rc://en/ta/man/translate/figs-metaphor]])
The abstract noun "love" can be expressed as a verb. Alternate translation: "but when we love people, we build them up" (See: [[rc://en/ta/man/translate/figs-abstractnouns]])
Building people up represents helping them become mature and strong in their faith. Alternate translation: "love strengthens people" or "when we love people, we strengthen them" (See: [[rc://en/ta/man/translate/figs-metaphor]])