Not every tenancy has these, and it may be something you may want to consider.
It is one way of agreeing a longer term tenancy whilst still having the option to end the agreement if it doesn't seem to be working out.
There's no standard format for a break clause. It may be that you can only use the break clause on or after a certain date. Some contracts only allow you to use the break clause at an exact point in the tenancy, but not after that date has passed.
As a general rule, break clauses are best avoided as they are prone to misinterpretation and often ineffective when the landlord tries to enforce them.
We suggest that if you do want to consider this option that you speak to your landlord and agree how to best move forwards.