If you're looking for a low-entry start to meditation, Headspace is a great little app. It starts off easy, with 10 10 minute guided sessions.
If you notice you've lost count, it's ok, just start from one.
If you notice you are lost in your thoughts, it's ok, just try to gently move focus back to counting and breathing. Do not "give extra energy on purpose" to thoughts that pop into your mind, just aknowledge them.
This is, IMO, is the core of the meditation routine - training on introspective perception and association of observation of personal thoughts with calmness.
The focusing of breathing is a hack on autonomic nervous system as I understand it. It's the only bodily function that one can control that backfeeds into the brain, and calming the breath can be used to calm the brain as well.
I'm not an expert, I've just read a few books that I've not double checked - if this is somehow wrong please correct me.