We can elongate any vowel in a syllable by using the ー elongating mark.

For example:

マーク：Maaku (Mark)

コーナー：koonaa (corner)

シャワー：shawaa (shower)

テーブル：teeburu (table)

コンピューター：konpyuutaa (computer)

Just like with hiragana, we can elongate a consonant by using the small tsu（ツ）, this time written with katakana, before the consonant.

For example:

カップ：kappu (cup)

クノック：kunokku (knock)

チェック : chekku (check)

In the last example チェック、you may have noticed that strange small ェ katakana after チ. Well, with certain syllables, the vowel sound can be changed by adding either a small ァ、ェ.

Take a look at these examples!

ソファー：sofaa (sofa)

チェコ：cheko (Czech)

ウィクトーリア：Vikutooria (Victoria)

ソフィア：Sofia (Sofia)

フィルム：firumu (film)

ビクター：bikutaa (Victor)

I included some names, so you can see how it works when Japanese people try to pronounce your name.

So, to sum it all up:

As for フ、we can add the small ァ or ィ to make it ファ(fa) or フィ(fi) respectively.

Then the other common katakana syllables are the following:

ティ(ti)

ウイ(ui, the French oui)

ヴァ(vi, pronounced like why)

Here are some more examples:

ウイルス

ヴァイオリン

アクティビティ