in = (with abl.) in, (with acc.) to, into, in : in loco - in the place , in Gallia , in Italia, in Italiam - to Italy
et = and : Italia et Gallia
ad = (with acc.) to : ad castra - to the camps, ad Caesarem
cum = (with abl.) with : cum legionibus - with legions
ex = (with abl.) from : ex eo loco - from this place
atque = and : filia atque filius - daughter and son
se = oneself, himself, herself, itself (other forms: sibi) : filius se lavat - the son washes (himself)
ut = how, as, when, in order that : ut erat dictum - as it was said
quod = what : quod erat necesse - what was necessary , quod est necesse - what is necessary
ab = from, by : legati ab hostibus missi - envoys sent by the enemies, ab equitatu - by the cavalry
qui = who, that, which (forms : quae, quos, quibus, quem) (relative pronoun) : filius, qui hic est - the son who is here
non = not, no : non est in Italia
esse = be (forms : esse, est, erat, sunt, esset, erant) : in Italia esse , est in loco, erat in eo loco
neque = and not, also not : neque saepe accidit - and it does not happen often
a = from, by (version of ab before a consonant) : a meridie (afternoon), a bello abesse - be absent from the war
quam = than, how, as (also form of qui) : citius quam pridie - faster than the day before
de = from, so, about : de causa rerum - about the reason of things
ac = and : filia ac filius
ne = lest, not : id ne accideret - lest it happens
si = if : si id facit - if he does it
aut = or : Caesar aut Cicero
is = he, that (forms: eo, eius, eorum, eum, eos, iis) : in eo loco ; neque is sum, qui - and I am not he who
omnis = all (forms: omnibus, omnes) : Gallia est omnis divisa - Gaul is all divided , omnis locus
castrum = camp : ad castra venit (comes)
hic = this (forms: his, hoc) , here : hic est quaestio - here is the question
res = thing (forms: rebus, re, rei) : res publica - republic, public thing
causa = cause, reason : causa rei - the cause of the thing
per = through : per Italiam - through Italy
locus = place (forms: loco, locum, locis) : in loco, in eo loco, locus citatus
hostis = enemy (forms : hostium, hostes) : castra hostium , hostis Caesaris

prepositions : in, ad, cum, ex , ab, a, de, per
conjunctions : et, atque, ut, neque, quam, ac, ne, si, aut
pronouns : se, quod, qui, hic, is
adverbs : non
verbs : esse
adjectives : omnis
nouns : castrum, res, causa, locus, hostis

Notes :
The preposition a is written as "a" before a consonant, "ab" before a vowel, but sometimes also before a consonant

The verb esse (to be) is most frequent Latin verb and it is highly irregular. Its most frequent forms are:
est - 3rd person singular present tense (is) , sunt - 3rd person plural (are), erat - 3rd person sing. imperfectum (was), erant - 3rd person plural imperfectum (were), esset - 3rd person sing. subjunctive imperfect

Nouns belong to different declensions, their forms can be found at the link below:
Declensions :
I declension: causa f (causae)
II declension: locus m (loci), castrum n (castri)
III declension: hostis m (hostis), omnis
V declension: res f (rei)

Hic and ille are demonstrative pronouns.
Conjugation of Latin verbs, including sum.