is a verb used to connect between words in a sentence (English).  This linking verb connects the subject with the pronoun (pronoun) or adjective (adjective) which describes the actor or subject.  Linking verbs are also often referred to as connecting verbs.  In its use, linking verbs consist of 3 types, namely verb of being, verb of be and verb of sensation.  
these linking verbs include all forms to be 
i
am
is
we
are
do
does
can