Double consonant - 促音(sokù òń), the smaller つ(tsu)

Pronouncing double consonant - 促音(sokù òń), the smaller つ(tsu) -

When you pronounce this character, you want to break the word up. It’s almost like you’re putting a little space in between the consonants of the double consonant. For example:
1分(ìppun) → ìp_pun : 1 minute
がっかり (gakkàri) → gak_kàri : shocked and sad

Although the space isn’t written in, if you think of it this way, it will make your pronunciation a lot better.
It’s like you end the first part with a “p” sound, and begin the second part with a “p” sound. You kind of pronounce both consonants, separately.

The possible double consonants in Japanese are: kk, gg, ss, cch, tt, dd, and pp.
The consonants gg and dd are used for foreign words only.

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~Examples~
・一人っ子 (h(i)tòrìk_ko): The only child
・バッグ(bàggu): bag
・一緒(isshò): together, same
・こっち(koc/t_chì): this way, here
・ちょっと(chòt_to): a little, just
・ベッド(bèd_do): bed (European style)
・いっぱい(ip_pàì): many, a lot

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Some words change the meaning totally different with/without っ.

~Example~
知ってる(shit_tèrù): (I) know
してる(shitèrù): (I’m) doing

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Usually you‘ll see the small つ in between characters, however, in the casual language we often put it at the very end of a sentence or interjection (such as “Wow”, “Ew” etc) to emphasise a bigger reaction/ stronger intention.

Saying “What?”:
え？(e?): What? (with your mind relatively relaxed)
えっ？(et?): What? (with your mind shocked/surprised by something you just heard)

Saying “Yes”
はい(hai): Yes. (like when you just answer an easy yes-no question)
はいっ(hait): Yes (like when someone tries hurrying you up)

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A tongue-twister (or practise?!) with っ!
※ in Hakata dialect.

おっとっと取っとってって言っとったとに、なんで取っとってくれんかったとって言っとーと。
(òttotto tottòttè tte ittòttà tòni, nańdè tòttòttè kùrèńkàttà tò tte ittòòtò)
: (I’m) asking why (you) didn’t leave (any) Ottotto (a Japanese snack) (for me) even though (I) asked (you) to leave (some for me).

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Hope you understand the small つ better!