I have read about it on the website and have tested it, but I can't really understand the difference between the two nodes, can anyone explain it to me? thank you!

The difference is in the number blend parameters sliders you can control.

With blend sequence, you have access to a single slider and can only interpolate one input to the next input.
So let's say you have 5 inputs, a blend of 0.5 will get you 50% of input1 and 50% of input2, and a blend of 1.5 will get you 50% of input2 and 50% of input3.

With blend shapes, you can blend all the inputs together at the same time.
You can get 25% of input1, 25% of input2, 0% of input3, 25% of input4 and 25% of input5.

So, blend sequence behavior could be achieved with the blend shapes node, but you would have to write expressions in the blend weights parameters yourself.