The daffodils nodded their yellow heads at the walker meaning

This means that there is a breeze / the wind is blowing. Sorry if I'm wrong.

There is a breeze blowing.

Explanation:

This is a scene-setting descrubing a walking trail, a park, a garden along a sidewalk. Daffodils bloom in the very earliest part of Spring; late February, early March. That they are "nodding" their heads could mean there's a soft breeze blowing. That there are walkers means it's probably a temperate, sunny day. And that's DAY rather than night - probably early morning or noon time, when people like to walk.