Arabic is not so complicated or hard to learn and you can learn it. We can speak Arabic like other people can speak English or French or Italian etc....you should first learn grammer, how to make a sentence & components of a correct sentence "the verb, the subject..." .If you mean how to pronounce letters espesially strong letters (ط،خ،ض،ظ،ح ) that can be easy by talkin' in Arabic to Arab people. By the way, your Q isn't correct, we say :كيف يمكن للناس التحدّث بالعربية؟

as each language it seems hard for foreign speaker but easy for a native speaek..i mean arabic language is not that complicated ..and i have to say that each arabian country has a different form of arabic ..i mean for example in libya (car means سيارة while in egypt it means العربية) another example in libya (i want )means أنا نبي while in egypt they say أنا عاوز or أنا عايز) but in the end they all speak arabic... also i want to say that your question can be formulated another ways...for example:- كيف يستطيعون التحدث بالعربية كيف يستطيعون التكلم بالعربية كيف يقدرون على الكلام بالعربي and a lot of these forms you will find in this amazing language

Do you mean how people can learn Arabic or how Arabs talk to each other? Arabic is like other languages can be learnd, can be used to communicate and also have lavish meaning... just tray to know how to learn it correctly. best wishes