So, let's say you have written a big essay or something. It's many pages long. So you put all those papers on a desktop and each paper has a number to identify it. Let's say each paper has a number, 1, 2, 3, etc. Each paper tells you what paper comes next, so in paper one it says paper 2 is the continuation of the paper. This is so that you will know what paper comes after the next.
So page 2 comes after page 1. Okay? Get me?
That is the basics of a linked list.
Now.
Even though the first paper is numbered 1, we don't know it's the first paper, so we have another list. An index paper. In that index, there are two lines: first and last. For first, it says 1. Why? Because 1 is the first paper on the essay. So first actually tells you the position (or index) of the first paper of your essay. But it only says WHICH paper is first first paper of your essay.
The last tells you what paper is the last paper of your essay. If the essay is 10 pages, then it will say 10. The index or id of the last paper.

Remember now: each paper also holds information about which paper comes next. So if you read first and find it's paper 1, you pick up paper 1 and it says next comes paper 2 and paper 2 says next comes paper 3 and so on until the end.

If you read the last in the index and it says 10, you pick up the 10th paper and read it. But no paper comes next, because it's the last in the essay, so we can't go forward through there.

If you find that you want to change something, maybe add a paper to the essay at the beginning, you give it a unique id. Let's just say for sakes, 11. Then you must update the index so that it says the first paper in the essay is 11. Right? So paper 11 says that paper 1 is the continuation.

You can also add a paper as the last paper of the essay. Let's give it id 12. Now you look up in the index which paper is the current last paper. It says id 10. So we take paper 10 and add a line that says after this page comes page 12. Then you updated the index to mention that page 12 is the last in the essay.

Does all of that make any sense?