Once you get Ping activated, go into iTunes and tap on the Ping button. The first screen to load is your latest activity. Unlike the desktop version, you don't have to deal with being pushed to follow artists you don't care about and immediately see what your friends are doing. The tabs along the top link you to people who you follow and are following you, plus your own profile, much like its desktop sibling.
If you want to like an album, search for it. When you click on the album page, you will have a button indicating to like the entire album. That's the easy part. The tricky bit is liking an individual song. To do that, tap the song title like you're going to preview it. The song will expand, giving you a chance to either like it or comment on it.
The biggest asset Ping has provided is an easy way to keep a running list of music I want to buy in the iTunes store later on. Mobile iTunes lacks a wish list feature, which is a shame because there are songs that I hear on the radio or through Pandora that I want to buy, just not right now. With Ping, when I hear a song I want to buy later, I fire up iTunes, like the song through Ping, then add it to my wish list when I go back to the desktop version of iTunes.
I've found I use Ping more on the iPhone than through my iMac. There's still a lot missing from the service, and I don't see myself using it other than an adhoc wish list until Ping matures a bit more and allows you to share music beyond what's available through the iTunes store... like the Beatles. Ever hear of them?