what exactly is PLR?

PLR is private label rights - and generally they're articles where you are given the rights to re-write the article(s) however you want. Putting plr products on your blog certainly won't harm it - providing you do re-write them otherwise they'll be the same as articles on other sites.

There's good and bad about plr articles - I actually have hundreds on my computer and honestly doubt I'll ever use them - They're good if you struggle to write as they can give you a starting point - but they're bad cause sometimes they are not very well written at all and hard to understand or certain facts they make are wrong etc etc.

There's plenty of places you can get free plr just do a search online and you'll find heaps.

Having said all that - if you do plan on doing something like this - make sure you have the rights to change the article otherwise you might find yourself in a bit of trouble if you copy someone elses work etc.