When you put a link in your post, your blog (if it accepts it) send a ping to the site you linked and if it accepts it then you will have a backlink in the comments section.
Trackbacks are similar. In Wordpress for example you will see a space where you can put links directly to ping. our blog doesn't have to link to the other blog in the article itself. But the other blog has to accept it.
You can send a lot of trackbacks and pingbacks but you have to find the ways it doesn't look spammy, otherwise they will not be accepted.