The combinations bi, ci, fi, gi, ki, mi, ni, pi, si, wi, zi

Digraphs (letter-combinations representing single sounds) include ch, cz,
dz, dê, d˝, rz, sz. The combinations bi, ci, fi, gi, ki, mi, ni, pi, si, wi, zi plus a
following vowel, representing b′ (bj), ć, f′ (fj), g′, k′, m′ (mj), ń, p′ (pj), ś, w′
(wj), ź, respectively, may also be considered digraphs.

"The combinations bi, ci, fi, gi, ki, mi, ni, pi, si, wi, zi plus a
following vowel, representing b′ (bj), ć, f′ (fj), g′, k′, m′ (mj), ń, p′ (pj), ś, w′
(wj), ź,"? Does anyone can explain it to me? I can't get it not at all.

I'm not Polish, but I think all it's trying to say is that the combinations of letters shown, bi, ci, fi, gi, ki, mi, ni, pi, si, wi, zi, when used in a word, sound the same or similar to b′ (bj), ć, f′ (fj), g′, k′, m′ (mj), ń, p′ (pj), ś, w′ (wj), ź.

Examples:

Biało ( White ) The 'bi' combination in the word sounds the same as b' ( bj )
Ciało ( Body ) The 'ci' combination in the word sounds the same/similar as Polish letter ć as in cześć.
Firma ( Firm ) The 'fi' combination in the word sounds the same as f' ( fj)
Słoń ( Elephant ) The Polish letter ń in the word sounds the same as letter combination 'ni'. It is pronounced similarly to the 'ni' in the English word ' onion '.

Siedem ( Seven ) The 'si' combination in the word sounds the same as Polish letter ś.

Maybe someone can explain this better, but hope it helps.

Note that "i" here is only a sign of softening the previous consonant and then goes always a vowel. So for example niebo (there is no ń initially) and słoń (not initially - midword or final position) sound the same. "F" in the word Firma may sond a bit soft because of assimiltaion to the following sond, but here only spoils the clean orthographic rule.