Some adverbs look exactly like adjectives:
But the adverbs that do end in -ly follow 4 simple rules.
nice --- nicely
quiet --- quietly
beautiful --- beautifully
sole --- solely
Rule #2 - If an adjective ends in a consonant + y, change the y to an i before adding -ly.
easy --- easily
lazy --- lazily
Rule #3 - If the adjective ends in a consonant + le, drop the e and add -y.
simple --- simply
responsible --- responsibly
Rule #4 - If the adjective ends in -ic, add -ally.
basic --- basically
economic --- economically
historic --- historically
NOTE: Just like all adverbs don't necessarily end in -ly, not all words that end in -ly are adverbs.
Friend is a noun. By adding -ly, you turn it into an adjective -- friendly.
The list of adjectives that end in -ly is quite extensive, so please do not confuse these as adverbs. Here is a short list of the most common -ly adjectives.
Lonely, lovely, daily, elderly, yearly, monthly, weekly, and early.