Verb (type 1): to start, to begin, to commence, to go ahead.
Aloittaa is the causative aspect of the verb alkaa. It might be recognized from its -tta/ttä suffix which is attached to many causative aspect verbs in Finnish. Causative aspect verbs are used when one causes someone or something else to do or be something. An classic example of a common causative aspect verb is tutustuttaa (”to introduce”), causative aspect of tutustua (”to meet”).
Let’s translate the whole phrase, ”Aina voi aloittaa alusta” (”One can always start over.) [Literally ”Always one is able to start from the beginning.”]
Aina is an adverb that means always.
Alusta is the elative singular form of the noun alku (note the consonant gradation) which means ”start,” ”beginning” or ”inception.” In the elative, alusta means ”from the beginning.” (Aloittaa alusta is a common phrase that means ”to start from the very beginning” or ”start over.”)