My website is verry slow, can you help me with this?

I don't know what to do about it because I don't have the knowledge to fix this. I tested  every page and they all load slow, but the slowest one is the homepage. From the recommendations I received, I should start all over with all the work done so far, in addition to optimizing the images that I don't know how much will help, there are also aspects related to java and css, and I have to make some cleaning here to.

Largest Contentful Paint is 20 seconds on mobile, verry slow and Total Blocking Time 1.420 ms.

I really do not think that It is working that slow because of some big images here and there, because even some pages on my shop that almost  have no images still take very long time to load. My account page has a performance of 51, my Contact page 43 performance, this is almost close to bad, so I am wondering If  some simple pages like this 2 pages tested, load so bad, what can I expect from a much more complex page.

I would appreciate if you can give some direction at least to make it work ok so google does not "hate me".

Hi Tahir,

Thank you, I added the plugin with all the settings. Verry small improvement. My account page has gone from a performance of 51 to 56, this is the small improvement. 

My contact page has gone down from 43 to 36. My home page works really slow with so many red warnings that I do not even want to count.