https://ibb.co/yfNV4dm This is a basic comparison of all the mechanisms of SN2/SN1/E2/E1.
E2 stands for elimination (2nd order) and essentially is a reaction where a base eliminates a leaving group forming an alkene. It often competes with SN2 reactions as many nucleophiles are also good bases.
E1 stands for elimination (1st order) and is a reaction where a hydride on a carbocation is plucked off by a weak base, leaving an alkene. Usually E1 reactions look like SN1 reactions but they have no good nucleophile in solution.
This is something you could consider asking further for in person office hours as new mechanisms can get clarified a bit more quickly with verbal explanations.