I'm curious about the difference between "I do know" and "I know".
I am an almost newbie at electronics but I do know a few things
Here the OP has used "I do know". Why?
Simply put, "I DO know this" is used to emphasize that you know the thing you're talking about, whether or not you know anything else.
Look at the OP's entire sentence:
I am an almost newbie at electronics but i do know a few things
Here OP says that even though he is new to electronics, but he still knows a few things. Therefore, "I DO know" is used to emphasize the point that he "does know" a few things, in spite of him being an amateur.
On the other hand, "I know" is just a simple expression stating you know something. It doesn't talk about something which you might not know.
Suggest to take a look at this question. The answer explains the phrase "as far as I know" (among other things), and uses this sentence:
Similarly, as far as I know means to the extent that my knowledge reaches—that is, “I do not claim to know everything about this topic, but what I do know is this ...”
See here how "I do know" is used to imply that you do not know everything about the topic, but you something, and that something is...