I seem to be answering some of the same questions about knowledge multiple times, so I thought I'd try to bring them together under one heading.
How do we know things?
We learn things (that is, come to know them) by using our senses and our brain. We observe things and draw rational conclusions based on these observations. Things that are true can be shown to be true; that is, they are confirmed by repeated observations. When we have sufficient confidence that something is consistently true, we say that know it.
This is not to say that we claim 100% certainty, however. For example, we observe that the sun rises in the east. Repeated observations confirm that this happens every morning. It's possible that the sun could rise in the west, but this would violate everything we have learned over the generations about the laws of physics. So it's extremely likely that the sun will always rise in the east; we can say this will a very high degree of confidence. Our degree of confidence is so high we are comfortable saying that we KNOW the sun will always rise in the east.
If you do not agree with my framing of knowledge and how we know things, please offer an alternative conception, along with any objection you may have. That way, we can compare the two conceptions to see which better addresses the objection, and makes the most sense in general.