Here we have some links to start revising the basics... verb to be, present simple, and present continuous...

http://www.agendaweb.org/verbs/tobe-pronouns/index.html

http://www.agendaweb.org/verbs/tobe/

http://www.agendaweb.org/exercises/verbs/to-be-forms

http://www.agendaweb.org/exercises/verbs/tobe-present.htm

http://www.englisch-hilfen.de/en/exercises/structures/contracted_forms_be.htm

http://www.focus.olsztyn.pl/en-exercises-for-present-simple.html#.VuhqXvmSzrU

http://www.perfect-english-grammar.com/present-simple-exercise-11.html

http://www.perfect-english-grammar.com/present-simple-exercise-1.html

http://www.perfect-english-grammar.com/present-simple-exercise-2.html

http://www.perfect-english-grammar.com/present-simple-exercise-3.html

http://www.perfect-english-grammar.com/present-simple-exercise-4.html

http://www.perfect-english-grammar.com/present-simple-exercise-5.html

http://www.perfect-english-grammar.com/present-simple-exercise-6.html

http://www.perfect-english-grammar.com/present-simple-exercise-7.html

http://www.perfect-english-grammar.com/present-simple-exercise-8.html

http://www.perfect-english-grammar.com/present-continuous.html

http://www.perfect-english-grammar.com/present-continuous-exercise-5.html

http://www.perfect-english-grammar.com/present-continuous-exercise-6.html

http://www.perfect-english-grammar.com/present-continuous-exercise-4.html

http://www.perfect-english-grammar.com/present-continuous-exercise-3.html

http://www.perfect-english-grammar.com/present-continuous-exercise-7.html