You can find mblogs using the simple and quick fields (keywords & categories) under the "Basics" button, or the powerful and comprehensive fields under the "More Search Criteria" button, or even a combination of both if you prefer.
If a button starts with a "+", then you can click on it to expand and reveal its search features, somewhat like peeling back an onion. If a button starts with a "-", then you can click on it to collapse and hide features to make your display less busy and confusing. Tip: click the + buttons for selection conditions you plan to use and click the - buttons for those you don't plan to use.
To learn how each selection condition works, mouse over the blue words of the selection. If you need more help, click the words.
Tip: Experiment. You cannot hurt anything by trying out all kinds of searches.