How to code with Email Marketing?

I'm starting with Email Marketing, I've never done it before and am facing  a world of difficulties. By the tutorials seen on the internet, I could draw the following conclusions:

• We use table so that it has a greater tolerance and thus does not have a layout break.
• We use class style with [], because it is more conventional * ex: tr[class="foo"]{}
• We use inline styles style="" because the email tools do not understand the <style></style>
• The web has evolved a lot, but the way to make code for email marketing is still well surpassed

If all of the above is right, I have some questions regarding responsive email marketing:

1) Trying to send a responsive email marketing template that I downloaded on the net works from a tool I used called PutsMail , but when I try via GMAIL directly called Gmail Append HTML , it does not get responsive. Because? What's the difference between the two?

2) How does Media Queries work with the style being inline? As far as I know there is no way to put media queries in inline style

3) In several email marketing tutorials, the instructor places <meta name="viewport" content="width=device-width, initial-scale=1.0"> in the head, if it's all inline, how is the meta tag inserted just for the layout view? in the end, who is going to send is the meta tag of the site where the end user access, right?

Thank you!