During the halves various things can happen that delay the game... injuries, a dog runs on the field, whatever... the Ref keeps track of the time lost for those interruptions and adds that time to the end of the game.
I've been following the World Cup for many years now... and I also catch a few games here and there at other times... I've come to enjoy soccer, certainly not football but it's fun... but here's the 'quirky thing' about it, if you will... lot of the stuff that at first kind of bugged me... seemed odd.... I now feel just gives the game some it's charm, eccentricity if you will... it's not as 'rigid' as most sports... and I've come to like that about the game.
