Zero, first, second, third and mixed.

http://www.bbc.co.uk/learningenglish/english/course/intermediate/unit-24/session-2/activity-3

http://www.bbc.co.uk/learningenglish/english/course/upper-intermediate/unit-28/session-1

http://www.bbc.co.uk/learningenglish/english/course/upper-intermediate/unit-28/session-4

The first conditional is used to talk about possible future situations and their possible results.

http://www.bbc.co.uk/learningenglish/english/course/lower-intermediate/unit-23/session-2/activity-3

The main difference is to do with certainty.

http://www.bbc.co.uk/learningenglish/english/course/upper-intermediate/unit-21/session-1

Five different ways of saying if without using if.

http://www.bbc.co.uk/learningenglish/english/course/upper-intermediate/unit-18/session-1

http://www.bbc.co.uk/learningenglish/english/course/upper-intermediate/unit-8/session-1

http://www.bbc.co.uk/learningenglish/english/course/towards-advanced/unit-7/session-1

The second conditional is used to talk about impossible, unlikely or imaginary situations and their possible results.

http://www.bbc.co.uk/learningenglish/english/course/lower-intermediate/unit-24/session-2/activity-3

The third conditional is used for imaginary situations in the past and their imaginary results.

http://www.bbc.co.uk/learningenglish/english/course/intermediate/unit-9/session-2/activity-3

http://www.bbc.co.uk/learningenglish/english/course/upper-intermediate/unit-1/session-1

Would is used

• in the second and thid conditional,
• for the future in the past,
• in reported speech,
• for repetition in the past, and
• for polite requests.

http://www.bbc.co.uk/learningenglish/english/course/upper-intermediate/unit-4/session-1

Zero conditional is used to talk about things which always happen in particular situations.

http://www.bbc.co.uk/learningenglish/english/course/intermediate/unit-5/session-2/activity-3