Two prisoners managed to escape after the police truck carrying them crashed on the highway. One of them , Mr Sawazaki (?) is a gangster who has sent 10 opposite bosses to hospital. The other called "You" - our protagonist - is a con artist whose cheating profile has piled up to approximately 100 billion yen. Accidentally, "You" then becomes the new teacher for the nearby high school, under the new name Takeda Shindo, and according to a deal of "Hammer Session" with the headmaster.
The quality of manga readers can vary. The uploads are often done cheaply or as a serious hobby by a collective. Be aware that sometimes licence hasn't been given but the sites noted above, Manga Fox in particular, are extremely careful about adding and pulling mangas according to license agreements. So you shouldn't have to worry too much about the material being pirated. There are also translated works and non-translated. Amongst the translated works you will find that the quality of translation may vary according to the skills of the translators. Usually the works are perfectly readable anyway, with only a few added or dropped words or a word in the incorrect tense or with/out plurals. But sometimes the text becomes gobbledygook. In which case, either seek another version or give up and buy an official copy once a printed translation comes out. The other issue of note is you may need to expand the screen to read the text easily as sometimes the scans are minimised a little.
I find that if a page doesn't download properly or some other issue occurs (too slow or someone ordered the pages incorrectly etc.) with one reader then skipping across to another reader and picking up where I was is quite easy and rarely annoying.
Otherwise, enjoy and watch out you don't get too addicted you forget about the necessary things in life.