It's a long and deep story, but here are a few parts.....
Country blues started mostly with itinerant black musicians singing about their day-to-day lives. The style seems to go back to the slave worker chants back when this country still had slavery. After the Emancipation, the roving musicians usually performed with banjo or, more so, the guitar. Mostly African-Americans from farms with acoustic guitars.
Blues is more associated with black performers.
The best example of country blues, I think, is Robert Johnson.
The origins of country music are even harder to explain - it's a big mixture, really - but the two most important country artists, Jimmie Rodgers and Hank Williams, Sr., put a lot of country blues into their music.
REAL country music is really just the white man's blues.
The music of Hank Williams, Sr. is really the essence of country music.
I hope this is a helpful start, Fabio.