Upgrading front suspension for an entry level MTB I recently bought a used hardtail MTB (my first bike ever) with Shimano's Acera groupset, double-wall wheels, but the front SR Ssuntour suspension has only 30 mm travel, which isn't enough for riding trails (I guess).
My question is :

Do I stick with the usual fork until I gain some skills ( I'm a complete beginner )
If not : is it as simple as replacing the front suspension with another one that has longer travel and then I'm ready to go, do forks need certain compatibility with other parts.

Thanks for your time !!!
Buying bike then immediately trying to upgrade components is a mistake. It would have been better to take all the money available for post purchase upgrades and putting it into just buying a higher specification bike in the first place. Components cost significantly less when purchased as part of a whole bike.

is it as simple as replacing the front suspension with another one that has longer travel

No, it isn't. A longer travel fork needs to be longer to accommodate more wheel movement, the frame needs to have a higher headtube to accommodate the longer fork without altering the headtube angle. Additionally there are compatibility issues with headset bearing sizes. Inexpensive frames use headset bearings that are the same size, better forks use a larger lower bearing.
Ride the bike, save up money, buy a better bike when your improving skills and finances allow.