Does it means a verb that should be used with a subject that is second-person and singular? What does "future active indicative" mean?
For example, I know "acuēs" roughly means "sharpen", but what's the right context? Does it means "(would like to) sharpen (you in the future)"?
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Each of the adjectives you list tells you a little more about how the verb is being used.
Second person specifies person; it tells you that the subject of the verb is "you." If the subject were "I" or "we" the verb would be "first person" (acuam or acuémus), and if the subject were "she" or "he" or "they" it would be "third person" (acuet or acuent).
Singular specifies number; it tells you that the subject is one person ("you, Kay, and nobody else"). If the subject were "you, Kay, and your brother, Englebert," then the verb would be "plural" (acuētis).
Future specifies tense; it tells you that the action hasn't happened yet. If you were talking about sharpening something yesterday, the verb might be "perfect" (acuistī) or "imperfect" (acuēbās) or "pluperfect" (acuerās) depending on other things about what you wanted to say). If you were talking about something you were doing right now, the verb would be "present" (acuis).
Active specifies voice; it tells you that the subject is doing the verb rather than that the subject is having the verb done to him/her/it. If you were talking to a pencil, you might use a "passive" verb instead (acueris): "Pencil, you're going to be sharpened."
Indicative specifies mood, but it's a little tricky; it basically tells you that you're talking about something that's happening in reality as opposed to something that might happen or might have happened, in which case you'd use the "subjunctive" (acuās, acuerēs, acueris, or acuissēs), or something that you're ordering somebody to do, in which case you'd use the "imperative" (acue or acuitō). That's an oversimplification, but it's probably close enough for government work. (Note that there's no such thing as a future subjunctive, and the future imperative is pretty rare.)
