I started looking up something on my computer, and ended up watching something completely unrelated on YouTube.
ーI started looking up something on my computer, and ended up watching something completely unrelated on YouTube.
「コンピューターで何か調べてたら、全然関係ないものをYouTubeで見始めてしまった」
to look up で「調べる」
to end up で「最終的に〜になる」
completely unrelated で「まったく関係がない」
ご参考まで!