It will become as a series to talk about MORPHOLOGY.
First of all we have to talk about the morpheme; a simple definition could be like the following:
The smallest unit of linguistic meaning or function……we can say that the word “predictable” consists of 2 morphemes: predict+ able
“unfortunately” = Un+fortune+ate+ly

So, morphemes can be a word or free (free morphemes: single morphemes that constitute words) for example: flower; is a single free morpheme..

or they can be bound (morphemes that can only occur in words attached to other morphemes; they can be called as affixes and they are of 4 types but the most common types are: prefixes(un-) and suffixes(-able)), and all of them will be described later………

NOTE: when a root morpheme is combined with affix morphemes it forms a stem; usable (use+able=stem) other affixes can be added to a stem to form a more complex stem; unusable (un+use+able)…

to be continued :wink