Kaf/khaf (כ) makes the same sound as het (ח) in Modern Hebrew when it's soft, but the distinction is that in hard positions כ, also written כּ in these instances, with a dot in the centre space, makes a /k/ sound. Traditionally soft khaf is pronounced further back in the thoat, but that distinction has been lost in common speech.
Not much... at the end of a word they do diffrent things. The כ sounds like CH/CHA and the ח sounds like ACH (EG. תפוח = apple = Ta-pu-ach) (EG. לך = (for) you = le-cha) (EG. איך = how = e-ch)
not the best exemples but that what I could think right now... Anyway at a middle of a word it is only memory
13mK1 actually a כ without a dot or דגש in it sounds the same as a ח and with a דגש, it sounds like 'k'. it's just people usually don't specify unless necessary, especially on keyboards. (it would only be necessary if there are two possibilities that have different meanings or uses)
in short, it's because it also doubles as two separate vowels. in more detail it's because in Hebrew vowels are in the form of stuff called 'נקודות' and the letter 'ו' can only really be a letter, but it's just that there are two 'נקודות' that look similar to 'ו' but have a dot in one of two positions. the thing is that on a keyboard, you can't write 'נקודות' without the hassle of a lot of copying and pasting and even on a pencil and paper, people typically don't write 'נקודות' unless not specifying which one leaves various options that can mean different things