When I create a work and upload it online, terms and conditions of many sites ask for me to transfer my copyright to the site. Does that mean I lose all those rights in them for the future?
It depends on the terms and conditions of each licence and whether the rights are granted on an exclusive basis or not. In any event, any contractual clauses which are unclear will be interpreted restrictively, always in favour of the author. A licence will never cover means of exploitation unknown at the time of licensing. Moral rights, as well as remuneration rights, will remain at all times with the author (regardless of any contractual clause they have signed).
Each time a work is reproduced, two types of copyright are generated, which can be collected by the author: mechanical (or reproduction) rights and public communication (or performance) rights.
In such cases, it is important that the rights holder seek advice. At EKKI we can provide it to you by contacting firstname.lastname@example.org.