Also known as a pure guarantee (www.practicallaw.com/6-107-6675). The guarantor promises to see to it that the principal (or underlying obligor) will fulfil its obligations under the primary agreement. If the principal then fails to fulfil its obligations, the principal will be in breach under the primary agreement and the guarantor will automatically be in breach of its obligations under the guarantee.
This type of guarantee is a secondary obligation so the guarantor's liability only arises if the principal fails to perform the guaranteed obligations and the guarantor is only liable to the extent that the principal is liable. For an example of this type of guarantee clause, see Standard document, Parent company guarantee from contractor's parent company: clause 2.1 (www.practicallaw.com/0-383-4705).