I used to be much troubled by questions of epistemology - how did we know that we knew something - how did we even know that knowledge was possible?
As far as I could see, there seemed no way that anything could be known.
But nowadays I am no longer plagued by such nihilism - and this is the solution I have worked-out (it seems valid enough to be going on with).
1. God knows - because he is the creator
2. We know because we are God's children
Explanation: We are God's literal (not symbolic) children - and therefore have inherited something of God in us, including the knowledge of the creator.
This establishes that validity of human knowledge is possible; because we have somthing of the creator (who made things) in each of us.
There remain many questions about explaining or deciding between disagreements in knowledge claims, errors, imprecision, uncertainty, changes etc.
But I find that the above simple epistemology does most of the heavy lifting in getting the weight of solipsism off my shoulders.
(Solipsism is the belief, or perhaps rather the fear, that I am the only thing which exists; and everything else is just in my mind.)