As you might have learned by now, Belgium is basically two countries in one. Are you in Flanders or in Wallonia? If you are in Flanders, you can find a list of teams using this tool (select your region and 'clubs met renners'):
Then select a team near you and send them an email to find out if you can train with them.
If you want to enter races, you can start with pure amateur races (usually no licensed riders). You only have to turn up to ride. A calendar can be found here (races from may-september, so the calendar is empty now): http://www.wielerwedstrijden.be/KALENDER/tabid/1704/language/en-GB/Default.aspx
You can also try Gentlemen-races (amateur races sanctioned by the Flanders Cycling Federation aka Vlaamse Wielrijdersbond), which are for non-licensed riders. For those races, you have to buy a day license for 5 euro's + an entry free. There may be special entree requirements (only for people who live in a certain region for instance), so make sure you are allowed to compete. The Calendar of races can be found here:
The pure amateur races are usually up to 50 km's. If you want to go up to 100 km's (and against better riders), you can ride cat 1.18 (up to 80 km) and 1.18 open races (80-100 km). You can ride with a 10 euro day license + entry fee.
If you live in Wallonia, you can look for a team here: http://www.fcwb.be/clubs.asp
Then get them to help you, since my French is horrible
PS. I just googled and translated this for you, I don't have any experience racing in Belgium.