Are you referring to form 8332? If you and the other parent are divorced or never married and live apart, then if the 8332 is signed by the custodial parent, the "other" parent can get the child tax credit or the credit for other dependent--depending on the age of the child. The custodial parent retains the ability to file as head of household, get earned income credit and get the childcare credit.
<a rel="nofollow" target="_blank" href="https://www.irs.gov/forms-pubs/about-form-8332">https://www.irs.gov/forms-pubs/about-form-8332</a>
<a rel="nofollow" target="_blank" href="https://www.irs.gov/pub/irs-pdf/f8332.pdf">https://www.irs.gov/pub/irs-pdf/f8332.pdf</a>
On the other hand, if you and the other parent live together, no document is required. Either one of you (but not both) may claim the child. You may decide between you which one will claim the child. Only if you can’t agree, do the IRS tie breaker rules apply, to see who has first choice. It may be worthwhile to prepare trial returns, both ways, to see which way the family comes out best. This tool may be useful: https://turbotax.intuit.com/tax-tools/calculators/taxcaster/?s=1.
The interview is confusing (it's designed for divorced parents, who are allowed to split the child). The second parent should not enter the child, at all.