SUMMARY FOR –LY:

1. -n, -an, -on, -en

These are standard suffixes to form adverbs of manner. Use them with adjectives according to the link vowel of their plural forms.

-they must be used with adjectives ending with -os, -es, -ös, -s!
-with some adjectives that end with ú, ű!

Examples:

békések > békésen = peaceably
szépek > szépen = beautifully
alaposak > alaposan = thoroughly
bátor – bátrak > bátran = bravely
vastagok > vastagon = thickly
egyoldalúan = in a one-sided way
egyértelműen = unequivocally

Exceptions:

lassú > lassan = slowly
hosszú > hosszan = for a long time
könnyű > könnyen = easily
szörnyű > szörnyen = terribly
nagy = big > nagyon = very

2. -lag, -leg

These suffixes are used with:

-adjectives ending with –i
–some adjectives ending with ó, ő, ű
-and with some more adjectives

barátilag = amicably
elvileg = theoretically
állítólag = allegedly
ellenkezőleg = on the contrary
valószínűleg = probably
aránylag = relatively
végleg = definitely
tényleg = really, truly

3. ul, -ül, -l

These suffixes are used with:

–languages spoken/written/learned by someone
-adjectives with these privative suffixes: -talan, -telen, -atlan, -etlen
-and some more adjectives

Beszélek olaszul. = I speak Italian.
Németül írok. = I’m writing in German.
Angolul tanulok. = I’m learning English.
aránytalanul = disproportionately
védtelenül = helplessly
akaratlanul = unintentionally
kelletlenül = reluctantly

Besides, the adverbs well/right and badly/wrong are formed with these suffixes, too:

jó > jól = well/right
rossz > rosszul = badly/wrong