Right, quite often the two dots in ё are omitted. Normally it does not cause any inconveniences for Russian native speakers, but sometimes it may cause a great messб for example, все (all the people, all things in a bunch) и всё (everything), мел (chalk) and мёл (he swept). I try to use ё when writing or typing.

for example, in the books of the letter "ё" really write "е" To understand this, you can guess from the substance of the proposals, or just to know the concept of certain words (sorry for my terrible English>. <)

Thank you all !!

While you learn Russian asking your interlocutors to use "Ё" in your conversation. It will bw better for you. Later you could understand the difference between Ё and Е by intuition.

It is true, Russians usually omit the two dots of "ё" in informal texts (Internet conversations, informal letters and etc.), but never omit line of "й".