When you're very still and quiet, then observe and notice how there is this nearly constant internal chatter going on -- one is thinking. As one thinks certain things, this generates emotional energy in the muscles of the body according to the 'way YOU feel' about what you are thinking. This thinking and changing one's vibration with an emotional signature is basically - being identified with one's reflection - or with one's personality -- a capability inherent in how our brains are built.
So now all that to see what not-surrendered is. Not surrendered is engaging in the mind-voice, the story telling, thinking, being identified with all that and allowing those feelings to happen. Surrender, and it's a practice, not a one-time thing, is like meditation, you work to become the still observer, quiet in thinking. So it's much like observe you are thinking, be WILLING to set all that aside and just sit in silence, it helps to have a focal point, such as feeling your breathing. Then you feel your breath go in and out, and before you know it, seconds actually, the mind-voice has started up again, and you have totally forgotten about feeling your breath (which doesn't require thinking). Then you give yourself a reminder, I don't need to think right now, I’m meditating, and you return to feeling your breath. And so you repeat this for about an hour, good to do it each day and twice a day if possible. This is 'surrender' practice. In a nutshell it's about not engaging in the fun you get out of talking to yourself (internally). I mean we do the story telling, chattering, emoting, because WE GET SOMETHING OUT OF IT. What we get out of it is the feeling this is US, that we are alive in this manner. So then you might imagine, it's kind of scary to totally 'shut-up' the first few times, because it's like we don't feel alive if we can't hear that echo of thought going on constantly inside our head.