It can be difficult to put a finger on what the Alexander Technique is and how we frame our thinking in the beginning is important. So...

Consider this:

Bodies are full of habits and in general habits lead to excess muscular tension. Which lead to strain. Which may eventually turn into pain.

Try this:

Squeeze your fist.
Now stop squeezing.
Squeeze again, Let go again.
Notice that by stopping, your hand naturally balloons up a bit.
It's like pushing on a spring and then letting go.

Now direct your attention to the place where your spine + skull meet.
It's just behind the soft palette.
In between the ears.
In front of the base of the skull.

Assume that that place is like your squeezed fist.
Rest your attention there.
Can you allow it to do less?
To free up?
To expand?

Imagine the length of the spine.
The width of the shoulder girdle.
And the easiness in the glutes and quads.

Going through this simple thought process can have a profound affect.

Try it while sitting at the computer, standing in line at the grocery store, opening a jar, or in downward facing dog.