English is a very flexible language and you can build on your vocabulary and learn how to make new words.
One way of doing this is to add prefixes (such as dis, pre or co) before the word.
Here's a list of common prefixes with their meanings and some examples.
anti (= against)
autonomous, autobiography, automobile
bi (= two)
co (= with)
contra (= against)
de (= remove)
dis (= not)
il (= not)
im (= not)
inter (= between)
misinform, misbehave, misunderstand
multi (= many)
non (= opposite)
out (= more than)
over (= too much)
post (= after)
pre (= before)
re (= again)
sub (= under)
super (= higher/improved)
trans (= across)
uni (= one)
under (= not enough)
You can also make new words from the words you already know by using different endings. For example, "The person who employs me has a fast car". You can make this sentence simpler, by replacing "the person who employs me" with "my employer". This gives you "My employer has a fast car."
In English you can make nouns from verbs (to employ gives employer and employee). You can also make verbs from nouns or adjectives: government gives to govern, modern gives to modernise and so on. Learning what endings you can put on words means you can expand your vocabulary and say what you mean more easily.
Here are some common word endings:
-er /- or: a person who does something
adviser / advisor, teacher, learner
-ment: result of action
-ism: name of system or belief
-ist: the person who believes in the system
-ence / ance
-able / ible
-proof / resistant
waterproof, childproof, fireproof
alcohol free beer, nuclear free zone