I'm sure there is someone here who speaks your language

The part you showed us is called a suspension fork. Like in motorcycles it moves up and down to "amortize" (absorb shocks). "Travel" is how far the fork moves up and down. If it moves far the ride is softer, if it moves less the ride is harder.

The lock locks (stops) the movement completely so it doesn't move - the suspension is not active. It becomes basically a rigid fork, it does not "amortize" in this state.

It must be unlocked when you ride on rough terrain because it can be damaged if it's locked and you hit bumps! It also has to be unlocked to "amortize" properly. That is what the suspension fork is designed to do. When you ride on smooth road you can lock it. When it's locked the ride is more efficient on smooth roads. That's because some of the energy of pedaling is wasted in compressing the fork.

Most of the time you don't need suspension when riding on smooth roads so you may lock it.

You don't have to lock it if you don't want to. It's OK to ride with active suspension on smooth roads. You can decide what you like better.

The travel adjustment also depends on what you like. If you ride on very bad, rough terrain or if you jump over obstacles then long travel is better because it absorbs the shock better.

In most other conditions short travel is enough.

You don't have to lock it if you park your bike.

You can adjust travel when riding.

I'm not sure if you can activate the lock when riding.

My advice is to have it always unlocked and set to low travel. It's possible you can hit some bad holes in the road when your fork is locked and you can damage it, if it happens too often.

I hope you understand what I said

Cheers!