Tout à fait directly translated would be 'all to do', how does this get inferred as 'absolutely'?
je m’en fous directly translated would be 'I am in craziness', how does this get inferred as 'I don't care'?
'Fais gaffe' directly translated would be 'Make/do a blunder', how does this get inferred as 'Watch out'?
« Tout à fait »
From http://micmap.org/dicfro/search/dictionnaire-godefroy/fait, "a fait" already meant "absolutely" in ancient French.
« Je m'en fous »
It's not "fous" as in "crazy" but rather the verb "foutre" (vulgar). It's vulgar for "Je m'en moque" (directly translated as "I'm laughing about it")
« Fais gaffe »
From https://originedesmots.blogspot.fr/2014/02/gaffe.html: "faire gaffre" means "keep guard" in ancient french
"tout à fait" can be translasted by absolutely, like "Be Chiller Too" Says.
"Je m'en fous" is pretty familiar. Think about a rough "I don't care"
"Fais gaffe" is equal to "fais attention" but is much familliar. You may translate this by "be careful"