I'm new on Upwork.
I'm looking for freelancers for a job.
I've sent a contact request to two freelancers, but I can't see anywhere if they received my request, and I can't understand when and where I'll receive their replies.
Welcome to Upwork, Daniele.
I don't see you as being a "dummy". You'll be able to see all communication in the applicant list for your specific job posting.
Finding the right worker is a bit of an art, and certainly can involve both initiating contact as well as waiting to be contacted.
Remember that the people that you contacted were likely shown first from a search, and thus are likely the most busy and typically most expensive. Some will reply to you, some will not, but in either case, you are more "selling" to them, (to take on your work), than they are to you.
When you post your job for others to find, now the selling process is reversed; the workers who find you are more selling to you, which puts you more in the driver's seat.
In short: patience has its virtues!
You said you 'contacted' some freelancers. By this, if you meant you 'invited' them, then I expect you will be hearing from them, if only to decline your invitation, because how quickly one responds to invitations is a factor in computing freelancer Job Success scores. Going forward, for quickest result, invite mainly freelancers with 24 hrs response time in their profile. Lastly, you have to allow for the possibility that there was an outage/interruption in Upwork messaging that delayed your invitation and/or the freelancers' replies.
"No good deed goes unpunished." -- Clare Boothe Luce