Donne-moi une allumette, s'il te plaît.

In an affirmative imperative (a command or request), French attaches object pronouns to the verb with hyphens. You can’t write Donne moi without the hyphen—it must be Donne-moi, Prête-moi, Montre-nous, etc.

French has two sets of object pronouns:

• Clitic pronouns like me, te, le/la, used in declarative sentences (e.g. Il me donne).
• Disjunctive pronouns like moi, toi, lui/elle, used:
  
  1. After hyphens in affirmative imperatives: Donne-moi.
  2. For emphasis or after prepositions: C’est pour moi.

In an affirmative command you always use the disjunctive form moi (and not me).

For regular -er verbs (like donner), the tu form in the present indicative is tu donnes, but the tu form in the affirmative imperative drops that final -s:

• Present indicative: tu donnes
• Affirmative imperative: (tu) donne

Exception: you add the -s back if the verb is followed by en or y (e.g. Vas-y).

Literally, s’il te plaît means “if it pleases you.” In everyday speech it simply functions as “please” when making a request. It softens the command and is polite.

• s’il te plaît uses the informal pronoun te/tu. You say it to friends, family, or anyone you address with tu.
• s’il vous plaît uses the formal/plural pronoun vous. You say it to strangers, elders, or groups, or whenever you use vous for respect.

Yes, you have flexibility:
• At the end: Donne-moi une allumette, s’il te plaît.
• At the beginning: S’il te plaît, donne-moi une allumette.
• In the middle (less common): Donne-moi, s’il te plaît, une allumette.

You can also omit it, but adding it is more courteous.

Unfortunately, the gender of French nouns often must be memorized. However, many nouns ending in -ette are feminine (e.g. la baguette, la fenêtre, la cigarette). When you learn allumette, list it as une allumette in your vocabulary.

Just change the number and make allumette plural:
Donne-moi deux allumettes, s’il te plaît.

Switch to the vous imperative form and use s’il vous plaît:
Donnez-moi une allumette, s’il vous plaît.