Maybe think of relays in terms of radio stations. Content creators send their content to them and they broadcast it to many people afterwards. Other syndicated stations pick up the original content but not all of them.

So it depends on to which relay you send your content to and from which relay you read other peoples content.

Looking at the relays other people use is a good starting point to find out what is actually going on.

A nice explanation can be found her:

naddr1qqxnzd3cxqmrjvehxqenxv3nqyvhwumn8ghj7un9d3shjtnwdaehgunpw35jucm0d5hszxmhwden5te0wfjkccte9ehhyctwvajhq6tvdshxgetk9uq3wamnwvaz7tmzd96xxmmfdejhytnnda3kjctv9uq3jamnwvaz7tmwdaehgu3wdamkuumrv9kx2tn0wfnj7qg6waehxw309aex2mrp0yhxummnw3exjcmg9ekxzmny9upzql6u9d8y3g8flm9x8frtz0xmsfyf7spq8xxkpgs8p2tge25p346aqvzqqqr4gux2x5sf

And as others said the #asknostr hashtag will enable you to find helpful people who are willing to answer your questions and help you in the onboarding process.