Learn French: Ok, ça marche !

Yes, the literal meaning of marcher is "to walk". However, in French, it is also the standard verb for "to work" or "to function" when talking about a machine, a plan, or an idea. Ça marche is a very common idiom meaning "That works for me" or "It's a deal".

Why does the c in ça have a little tail under it?

That mark is called a cedilla. In French, the letter c normally makes a hard "k" sound when it comes right before an a, o, or u. Adding the cedilla turns it into a soft "s" sound, so ça is pronounced like "sa" instead of "ka".

Is it a typo that there is a space before the exclamation mark?

No, that is correct French punctuation! In French, you must always put a space before two-part punctuation marks, which includes exclamation marks, question marks, colons, and semicolons.

Do French people really use the English word Ok?

Absolutely. Ok is used constantly in everyday, spoken French to show agreement. If you want a more traditionally French alternative, you can say D'accord.