The particle も is used in a similar way as は, to show the topic of the sentence. However, whereas は means “we are talking about this, and nothing else,” and can be used for contrast with what has been said before, も means “we are talking about this in addition to what we were talking about before.”
川田さんは社員です。内田さんも社員です。
Mr. Kawada is a company employee. Mr. Uchida is also a company employee.