Sure! Basically: the implant contains the uploaded minds of all the previous leaders of Lexa's people. While it's somewhat degraded from use, it essentially grants her the ability to interface with the previous commanders both actively and passively (some knowledge appears to come to her and other users of the implant just through existing, or thinking of it). The minds of the previous commanders are thought to be alive and living on, though it's implied that they only live on while the implant (... which is basically a computer chip) is active inside of someone.

Only someone biologically predisposed can use the chip: Lexa has black blood that grants her this ability. It's not clear as to why this is the case except that this black blood helped her people develop after a nuclear war on Earth. Basically, it's a trait that's been passed down through through her people, only not everyone has it (but all of them are biologically predisposed to resist radiation that comes with a nuclear war even a little bit).

Essentially: the implant just gives greater depth to Lexa's knowledge and has a bunch of dead people's minds uploaded to it, but it interfaces with its user, and the user is the one absolutely in control. It doesn't give her any powers, and it requires special Latin to remove without having to carve it out of her neck. Unless she's dead. I'd be taking her post death to explore the ramifications of that, but it would still (presumably) be in her neck.