Official CraftyJS API documentation doesn't helped me in that case
It's all there in this case, although distributed over several pages. Be sure to skim through the whole API to get a good overview of the available functionality.
What I need: large horizontal map (platformer)
See last example in Getting started.
What I need: ... camera, following the hero
Camera is referred to as Viewport in Crafty. See Crafty.viewport.follow()
Let me know if you have further questions.
Putting it all together:
Crafty.init();
Crafty.e('2D, DOM, Color, floor')
.attr({x: -400, y: 250, w: 850, h: 10})
.color('green');
var hero = Crafty.e('2D, DOM, Color, Twoway, Gravity')
.attr({x: 0, y: 0, w: 50, h: 50})
.color('#F00')
.twoway(200)
.gravity('floor');
Crafty.viewport.clampToEntities = false;
Crafty.viewport.follow(hero);
<script src="https://cdn.rawgit.com/craftyjs/Crafty/0.8.0/dist/crafty-min.js"></script>