Paul continues to give thanks for the believers at Thessalonica and praises them for their faith in God.
Here this means fellow Christians, including both men and women.
The word “we” refers to Paul, Silvanus, and Timothy but not the Thessalonian believers. (See: rc://en/ta/man/translate/figs-exclusive)
Not only through the activity of preaching God’s message. (See: rc://en/ta/man/translate/figs-synecdoche)
Possible meanings are 1) the Holy Spirit gave Paul and his companions the ability to preach the gospel powerfully or 2) the Holy Spirit made the preaching of the gospel have a powerful effect among the Thessalonian believers or 3) the Holy Spirit demonstrated the truth of the gospel preaching by means of miracles, signs, and wonders.
“how we conducted ourselves when”