たった is a common adverb in Japanese that originates from an emphasized alteration of 唯（ただ） ‘only’, ‘merely’.
たった keeps the same meaning of ただ in that it just expresses that something is ‘only (A)’, ‘just (A)’, or ‘no more than (A)’.
This nuance is usually used when the actual number of (A) is exceptionally low compared to the speaker’s expectation of anticipation.
たった will often appear at the beginning of sentences, and will either modify the whole sentence, or a specific number when followed by の and then that number.
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先輩（せんぱい）、たった今（いま）東京（とうきょう）駅（えき）に着（つ）きました。
Senpai, I arrived at Tokyo station just now.
僕（ぼく）、たった一人（ひとり）でここまで歩（ある）いてきたのかい？偉（えら）いね！
Kid, you walked here all alone? I’m proud of you!
クラスメイト全員（ぜんいん）を招待（しょうたい）したのに、たったの３人（にん）しか僕（ぼく）の誕生日（たんじょうび）パーティーにこなかった。
I invited everyone in my class, but only 3 people showed up to my birthday party.
このホテルからビーチまでの距離（きょり）はたったの１０メートルです！
It’s merely 10 meters in distance from this hotel to the beach!
As
たった is an adverb that is usually used for emphasis, it often accompanies other similar grammar patterns like だけ, しか, etc.
Fun-fact - The common expression ただいま ‘now’, or ‘I’m home’ may occasionally be seen in the emphasized form
たったいま. This is primarily when the meaning is ‘now’, or ‘just now’ (right at this present moment), rather than ‘I’m home’.
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その電車（でんしゃ）はたった今（いま）出発（しゅっぱつ）したので次（つぎ）の電車（でんしゃ）が来（く）るまで少々（しょうしょう）お待（ま）ちください。
That train has just departed, so please wait until the next train arrives.