A line of code, I do not understand. 1<

It's layer specifying using bit shifting. It's very well explained here.

It's a shifting operation. LayerMasks use the bits of an integer (4 bytes = 32 bits, thus you can have 32 layers) to store multiple layers in one integer efficiently. That means, you can combine any layers that you like and only need 4 bytes, i.e. a simple integer. LayerMasks.NameToLayer returns the index of a given layerName, for example you've got a layer called "myLayer" at the 9th position, which is, according to 0-based counting, the index 8.

That in turn means, if you want to use this layer in a LayerMask, you have to set the 9th bit of an integer.

Imagine you've got an integer, which is currently 0, that represents your list of layers (0 not set, 1 set)

0000 0000 0000 0000 0000 0000 0000 0000

You now have "myLayer" in the 9th slot in the layer list. According to that, you want the following LayerMask

0000 0000 0000 0000 0000 0001 0000 0000

As stated above, the method LayerMask.NameToLayer(...) returns the index (remember, it's 8) so you can now do the following. Start with 1 written in binary:

0000 0000 0000 0000 0000 0000 0000 0001

and shift it

once: 0000 0000 0000 0000 0000 0000 0000 0010

twice: 0000 0000 0000 0000 0000 0000 0000 0100

[...]

8 times: 0000 0000 0000 0000 0000 0001 0000 0000

Voila, you have the appropriate LayerMask for your layer.