http://www.grammar-quizzes.com/gerundex1.html
http://www.englishpage.com/gerunds/gerunds_infinitives_29.htm
Read the page and continue with the exercises: http://web2.uvcs.uvic.ca/elc/studyzone/410/grammar/gerinf.htm
Lots of Gerund Practice: http://www.grammar-quizzes.com/gerundsum.html