Before continuing we should agree on the gender of lauva
I guess it can be both feminine and masculine but to simplify things in this thread we should pretend that it's only feminine. Baltā lauva
is perfectly correct.
In English definiteness is expressed by using articles (a
are the indefinite articles, the
is the definite article). In Latvian there are no articles but we still have the concept of definiteness. Adjectives can have indefinite and definite endings. There is no difference between "a sheep" and "the sheep" in Latvian (in both cases it's aita) but there is a difference between "a white sheep" (balta aita) and "the white sheep" (baltā aita). So, when you use the definite article in English you'd also use the definite endings with adjectives, and when you use the indefinite articles you should use the indefinite adjective endings.
Indefinite adjective endings are the same endings that I (masculine) or IV (feminine) declension nouns have. Definite adjective endings are different. Personally I like this table
Let's say you want to describe the noun aita (singular/vienskaitlis, nominative/nominatīvs/N.) with the adjective balts (the root is balt). aita is a IV declension noun which means that it's feminine. Adjectives must agree in gender so the adjective must have feminine (sieviešu dzimte) endings. Now locate the endings: vienskaitlis / sieviešu dzimte / nominatīvs. There are two possibilities: -a (indefinite/nenot.g.) and -ā (definite/not.g.). So a white sheep is balta aita and the white sheep is baltā aita. Now try the plural endings: daudzskaitlis / sieviešu dzimte / nominatīvs: -as, -ās. white sheep is baltas aitas and the white sheep is baltās aitas.
To practice try translating these sentences:
The white flowers. (balts, puķe)
Black socks. (melns, zeķe)
Blue eye. (zils, acs)
Blue eyes. (zils, acs)
Tasty honey. (garšīgs, medus)
Loyal friend. (uzticams, draugs)
The best friends. (labāks, draugs)
The little brother. (mazs, brālis)
Also, please describe which declension nouns you think they are and which gender they are and describe how you found the endings you used.
(When you can do these, I'll give you other sentences in other cases)