German does not have the –ly distinction in English between an adjective and an adverb. You can use almost any adjective as an adverb without changing it, as long as it makes sense:

Das Pferd ist schnell.
The horse is quick.
Er rennt schnell.
He runs quickly.

The only thing in German that’s somewhat comparable to our –ly is the –erweise fomulation, which modifies an entire clause rather than just a verb or an adjective:

Es ist normal, dass wir um 7 Uhr essen.
It's normal for us to eat at 7 o'clock.
Normalerweise essen wir um 7 Uhr.
Normally we eat at 7 o'clock.

As in English, there are also some common adverbs that don’t map as directly to adjectives. They all work grammatically in the same way as their English equivalents, and they don’t take any case endings, so you just have to memorize them. Some of them you’ve probably seen already:

Time Manner Place
anfangs -- at the beginning
bald -- soon
bereits -- already
damals -- at that time, then
danach -- afterward
dann -- then
diesmal -- this time
einmal -- once
endlich -- finally, at last
früher -- earlier, previously
gestern -- yesterday
heute -- today
immer -- always
inzwischen -- meanwhile
jemals -- ever
jetzt -- now
langsam -- slowly
längst -- long ago
manchmal -- sometimes
meistens -- mostly, most often
neulich -- recently
nie -- never
noch -- still
nochmal -- again
nun -- now
oft -- often
schon -- already
sofort -- immediately
vorbei -- over, past
vorher -- previously, before
vorhin -- just now, a short time ago
wieder -- again
zuerst -- first, at first
zurzeit -- at the moment, at present
beinahe -- nearly, almost
besonders -- especially
bloß -- merely, simply, just
daneben -- besides, in addition
ebenfalls -- likewise, also
ebenso -- equally, similarly
eigentlich -- actually, in fact
fast -- almost
gemeinsam -- in common, jointly
gern, gerne -- gladly
hoffentlich -- hopefully
insgesamt -- in total, altogether
kaum -- hardly
leider -- unfortunately
mindestens -- at least, at minimum
nämlich -- namely
natürlich -- naturally
nebenbei -- by the way, incidentally
schließlich -- finally
sehr -- very
sogar -- even
sonst -- otherwise
teilweise -- partially
übrigens -- by the way
ungefähr -- approximately
ursprünglich -- originally
vielleicht -- perhaps, maybe
wahrscheinlich -- probably, likely
wirklich -- really, truly
ziemlich -- rather, quite
zufällig -- accidentally, by chance
zurück -- back
zusammen -- together
aufwärts -- upward
auseinander -- separated, apart
außen -- outside
da -- here, there
drüben -- over there
geradeaus -- straight ahead
hier -- here
hinten -- in back, at the back
innen -- inside
links -- left
nebenan -- next door
nirgends/nirgendwo -- nowhere
oben -- above
rechts -- right (≠left)
rückwärts -- backwards
überall -- everywhere
unten -- under
vorn(e) -- in front, at the front
vorwärts -- forward