Relatives Clauses: Theory and Practice.

Relative clauses are extremely useful in our everyday English. You must learn, first of all, the different relative pronouns. Once you master them, use them in relative clauses.

Video lesson about Relative Pronouns

Defining (specifying) vs Non-defining (non-specifying) sentences.

Video lesson for Advanced Learners

Some practice will be more than necessary. Here you are some and graded in difficulty :D

PERFECT ENGLISH caters for ordinary sentence construction practice.
OM EXERCISE includes definitions with relatives and sentence formation.
EGO4U includes explanation in English and activities.
AGENDAWEB offers assorted pratice including tests.
Explicación básica en español.