Epistemology is the study of knowing. It deals with the nature of knowledge, how do we know things, what do we know, why we know, is what we know true, and what are the limits of knowledge.
It is true that we know things. You know you are reading this. But what is the nature of what you know? Does it properly reflect reality (truth)? Is knowledge primarily gained through our sense experiences (empiricism)? Is knowledge primarily gained through reason (rationalism)? There is a priori knowledge or knowledge that is automatically known apart from experience and posteriori knowledge or knowledge that is gained from experience.
Generally speaking, epistemology deals with the nature of knowledge and not the how-to of knowledge. In other words, what is the relationship between truth and reality versus how do I build a cabinet.
Foundationalism is a subset of epistemology.