What it must contain
The funding body's full name, the grant or award number, and where relevant which author received it. Abbreviations alone are not enough — an indexing system matching your paper to a funder needs the full registered name.
Grant numbers must be exact. Funders track outputs against award numbers, and a transposed digit means your paper does not register against your grant. That has consequences at renewal, when you are asked what the last award produced.
Many funders publish required wording, and some mandate a specific phrase. Where they do, use it verbatim. Compliance is a condition of the award, not a stylistic preference.
Grant numbers are how funders match outputs to awards. A wrong digit means your paper does not count towards your own grant.
When there is no funding
Say so explicitly. "This research received no specific grant from any funding agency in the public, commercial or not-for-profit sectors" is standard wording and journals expect a positive statement rather than silence.
Silence is ambiguous — an editor cannot tell whether there was no funding or whether you forgot. Unfunded work is entirely normal and declaring it costs nothing.
Institutional salary is not usually declared as funding unless the journal asks. Specific internal awards or seed grants generally are.
Where it sits, and adjacent obligations
Placement varies. Most journals put funding in a dedicated section near the acknowledgements; some fold it into the acknowledgements themselves. The submission portal usually collects it as structured metadata too, which is what feeds funder reporting — fill both in, and make them consistent.
Funding disclosure is related to but separate from conflict of interest. Industry funding must appear in the funding statement, and if it creates a competing interest it also belongs in the conflict-of-interest declaration. Doing one does not discharge the other.
Check for an open-access condition. Many funders require the resulting paper to be openly available, sometimes within a set period and sometimes under a specific licence, and this can determine which journals you may publish in at all. That is worth knowing before submission rather than after acceptance.