Ok. Belgium has quite a few 'gold standards. As in beer that set the tone for the entire style. They basically define the style, so to speak.
Saison: Dupont saison
Strong golden ale: Duvel
Abbey beers: Westmalle, Rochefort, Westvleteren (v hard to find abroad), and Chimay are all excellent. If you have to pick one Westlveteren and Rochefort for quads, Westmalle for triple and dubbel. Chimay, anything.
Belgian pale ale (technically an abbey beer too): Orval (this is quite different and not for everyone. Must try tho).
Witbier (close cousin of weizen); St bernardus. Actually, anything you get from st bernardus will be more than ok. The witbier and the quad are probably their best.
Then we go to sours. Start with these
Gueuze: brouwerij Boom. Go for the regular one, take it from there. If you like the style and only if, then move on to things like 3 fonteinen and cantillon (can get pricey).
Flanders red ale: duchesse de bourgogne or rodenbach (classic or grand cru).
Belgian beers are mostly not hop-forward beers (think ipa). They are masters of yeast and fermentation and generally brew multilayered nectars that are to be zipped slowly, patiently, and carefully.
As they are not hop forward, quite a few of them can be stored for quite a long time, i'm talking years. In beer shops in belgiu and the netherlands it is quite common for you to be able to purchase quads by vintage.
See, certain flavours change with time. Some of them are welcomed and some of them are not. For instance, a hoppy IPA loses crispiness and bite with time, so that is not desirable. That is why you want your ipas fresh. But with other beers (quads, strong stouts, some sours) time helps flavours to evolve in a positive/desirable manner. Very, very generalized rule of thumb: dark strong (+10%) beers are ok to age. Many sours too.
They have a LOT of other outstanding brews i am not mentioning. I am just giving you a very summarized lay of the land.
This should be enough to get you started. Enjoy n cheers.