Showing order with thumbnail links

I'm putting together a little tutorial website, where tutorials should be read one by one, in a particular order. The tutorials are shown as thumbnails that can be clicked on, like this:

I want people to start with the link in the upper-left corner, then go to the right, the same way you read words. However, I'm afraid that's not obvious, and people are just clicking them randomly, which will definitely confuse them. (I don't really advertise this site very much, but I've had at least one person ask me what order these tutorials should be read in.)

So, my question is: How can I make it more obvious that these links should be clicked in order?

This is complicated by the fact that there are sections of links where the order doesn't matter. The Examples section contains similar links, but there is no inherent order. And the bottom of a tutorial link page might contain an Advanced section, where order doesn't matter there either.

Here's an example of a section where order doesn't matter:

In this section, people would have already gone through the tutorials and are coming here to look at examples, so the order they view these in doesn't really matter.

So I guess a more specific version of my question is: How do I show there's an order to the thumbnail links in some places, but not in other places?

If you want to look at the overall site, it's available at HappyCoding.io. I'd also love to hear any general feedback.