I don't understand German myself. I learned it at school, but forgot every word of it two years after I had left, and have felt much better ever since. Still, I did not want the people there to guess my ignorance; so I hit upon what I thought to be rather a good idea. I kept my eye on the two young students, and followed them. When they tittered, I tittered; when they roared, I roared; and I also threw in a little snigger all by myself now and then, as if I had seen a bit of humour that had escaped the others. I considered this particularly artful on my part.

I noticed, as the song progressed (я заметил по мере того, как песня продолжалась = через некоторое время; to progress — развиваться, двигаться вперед), that a good many other people seemed to have their eye fixed on the two young men, as well as myself (что довольно много других людей, казалось, не сводило глаз с юношей, как и я; to fix one`s eyes on — уставиться, впиться глазами). These other people also tittered when the young men tittered (тоже хихикали, когда хихикали молодые люди), and roared when the young men roared; and, as the two young men tittered and roared (и, так как эти двое молодых людей хихикали, хохотали) and exploded with laughter pretty continuously all through the song, it went exceedingly well (и разражались смехом почти непрерывно на протяжении всей песни, дело шло чрезвычайно хорошо/замечательно; to explode with laughter — разразиться смехом; громко рассмеяться).