To make a noun, adjective or participle feminine in Arabic we add the letter ة on the end which is called ta marbuta. Ta marbuta means 'tied-up t' because it resembles a ت (t) with it's two dots. It is the shape of ه (h) and it is pronounced as (ah) or just (a) on it's own or at the end of a word.
A male teacher is مدرس (mudarris).
So a female teacher is مدرسة (mudarrisa).
A male engineer is مهندس (mohandis).
So a female engineer is مهندسة (mohandisa).
It's really as simple as that, just add an 'a'!
The same goes for adjectives.
For example:
كويس (kwayyes) is an adjective that means 'good'. We can use it to describe a male person:
مدرس كويس (mudarris kwayyes) -- a good (male) teacher.
The adjective agrees with the noun. The teacher is male, so the adjective is male. So what if there is a female teacher? We say:
مدرسة كريسة (mudarrisa kwayyesa) --- a good (female) teacher.
We just add an 'a' on the end of the adjective too!
Remember that arabic doesn't have words for 'a' or 'is'. They're just left out.