I know there is a new law and the other answers are old. I am confused because I read somewhere that home mortgage interest up to $100,000 is deductible even if you don't use the extra money from a refinance for home improvements. Married filing jointly. Using standard deduction for federal but might have enough deductions for state of California, but not sure how to do the mortgage adjustment for California. I don't know what figure to input. Thanks.
That screen should have your ending loan balance at the end of the year (on 12/31/2018) for "home acquisition debt on date debt was last secured by home". If you entered that information when you entered your 1098 it should show up here and you won't need to enter or change anything on that screen.
The law that you stated about the $100,000 is the old law. Under the current federal tax code you can only deduct mortgage interest that is secured by your property and only when the loan proceeds were used only to buy, build or improve that property. The limitation is $1M for debt incurred before or on December 15, 2017 and $750k for debt incurred after that.
California allows the same $1M - you can confirm this on the CA FTB site here under "mortgage interest" https://www.ftb.ca.gov/current/Income-tax-reform.shtml