Receivers start with relative time checks for received signals aided by any still current satellite almanac info they may have from a prior session or other available location or time info (e.g. time or Mobile data/ wifi derived location data on a phone).
Any receivable satellite will give a quite accurate time signal and the receiver can then start to play with the subsequent signals to try to assemble a plausible set of 3D spheres from the relative delay of each time signal and assumptions about credible altitude /depth.
Each satellite also transmits a complete set of constellation almanac data so if a rough location is not not already solved the alamanc info becomes available after about a minute and tells the receiver where each 'visible' satellite should be in space at that moment.
With this info too the rough spheres solution becomes trivial and the receiver can now move to refining the location /altitude to a precision fix and maintain those updates in use.