Jared, I hope you bought it. If made right, it is really really tasty. If not, I can tell you how it is made, but be warned, it costs lots of time (you cook it until most of the water has boiled away, while constantly stirring, as it is prone to get burned on the bottom). Most people spend half a day making a big portion on open fire (because nobody has a stovetop on which a pan that wide fits) and then preserve it in jars. On the other hand, homemade tastes best, and then you can control the hotness (ljutenica can go from purely sweet to tabasco hot, depending on the type of peppers used) and the additions (pure liutenica is peppers and tomatoes only, but it also contains any veggies currently ripe in the garden which might spoil if not preserved quickly).
As for use, it is just a bread spread - or rather, it is the bread spread. A thick slice of semiwhite bread with with ljutenica is an iconic symbol of childhood for anybody who grew up between the 1950s and 1970s in Bulgaria, as that's what kids grabbed for a quick snack before running back outside to play. Traditionally, nobody includes it in any dishes. And nobody considers it a condiment. It is sometimes served as
meze, which is a kind of appetizer eaten when drinking strong alcohol, in order not to get too drunk. I guess that whenever you serve antipasti, you could also offer a dish with liutenica, it can be scooped from there and eaten pure or with black olives and/or cubes of feta cheese. If you want to add spices to it, fresh parsley is the traditional one.
On the other hand, although Bulgarian cuisine is somewhat on the simple side, with lots of tradition and not much experimentation, there are no hard rules (in the sense of the Italian rules to never use certain sauces with certain shapes of pasta). So you can use it in any capacity you like. I sometimes use it (without cooking it to a proper thick consistency) as a pasta sauce (no matter what shape of pasta, but psst, don't tell the Italians). Once I pureed feta cheese in it and filled a quiche with the result, it got quite tasty.
Of course, if you happen to cook a Bulgarian style dish, you can use it as a condiment served on the side. Or use it anywhere you'd use ketchup. As many Bulgarian dishes include cooked or pureed tomatoes, you can also try using some liutenica as a substitute, either adding water if you want to keep a runny consistency, or take advantage of the fact that it is thick and make a dish thicker or cook it for less time.