This I hope won't come across too broad of a question.
If you've been tasked with introducing testing process' for a web application developed in an 'agile' environment, released in 2 weekly cycles. but currently there is no framework in place. No documentation of existing features, test plans or much else for that matter. Then where do you start?
I've been thinking about this and I think the following are good starting points to consider:
Identify existing features: Rank for risk of breaking due to change and impact of breaking.
For high/medium impact/risk features: Identify how features should work. Create test cases detailing intended functionality. Create data to test. Identify where, when and how test should be done. Add to test plan.
To clarify, the objective is to introduce a framework which can be used for generating functionality tests for new features and regression tests for existing undocumented features. But not to test and document things for the sake of it.