Libido is the urge to have sex. It’s the engine of sexual activity
If you have a high libido sex is important. This often shows in the attention you pay to attractive guys and/or girls, in your interest in sexual stimuli (erotic stories, porn, the amount of sexual fantasies and daydreams etc.) and in your need to masturbate.
Libido differs greatly from person to person. When you start or have a relationship this is important to realise. Normally guys have a higher libido than girls, but in a relationship it can easily be the other way round.
Guys have their highest sex drive during their teens and early twenties, while women normally have the highest drive during their thirties.
Libido depends on physical factors, like testosterone. But mental factors also play an important part. If you are for instance used to paying attention to sexual stimuli around you, your sexual urge will increase. Experience also plays an important part. Bad experiences decrease your desire for sex, while good experiences make you long for more.
Normally it takes some time to learn how to handle your libido. You have to create the right mix between the urge to have sex, your ideas about a relationship and your values.