Overwhelmed Newbie questions

I’m not clear about the following…
a) What is the difference between a block and a hashtag. Why do I need to use a block. If I want to search in the text I’ve entered in logseq, I can just search using a hashtag?
b) I don’t get how Dario adds the image in this video at 1:43. Looks like he is taking a screenshot, and pastes the image in logseq. Is he using a special tool that can do this? I would think he needs ton/upload and select the image file from desktop? Logseq beginner's course (3/8) - Introduction to blocks and pages - YouTube at 1:43

Thank you…

I figured out the black vs hashtag difference!

Hi, to do the screenshot capture, he is using the inbuilt Windows tools - press Windows key + Shift + s
He is then simply pasting it with Crtl + v.

I think that is what he is doing anyway…