Arsenal got their first win in this year’s Champions League with a 2-0 win against Paris Saint-Germain on Tuesday night.
Last time, Arsenal had a 0-0 draw with Atalanta.
But at their home ground, called the Emirates Stadium, Kai Havertz and Bukayo Saka scored goals to make Arsenal win.
Manchester City also won their first game, beating Slovan Bratislava 4-0.
Dortmund beat Celtic with a big score of 7-1, and Brest won 4-0 against RB Salzburg.
Other games had Barcelona winning 5-0 against Young Boys and Inter Milan winning 4-0 at home against Red Star Belgrade.
Bayer Leverkusen won 1-0 against AC Milan with a goal from Victor Boniface.