If your business is a sole proprietorship or single member LLC that you are reporting on SCH C as a physical part of your personal 1040 tax return *********AND******** you were "officially" open for business on or before DEC 31 of 2019, you'll report $0 for business income, and whatever you spent on business expenses, as expenses. Yes, it's that simple. Of course, with no business income to deduct those business expenses from, it won't make a penny of difference to your tax liability. But those "unallowed" expenses will be carried forward to 2020 and deducted from your 2020 business income *IF* you have the business income in 2020 to deduct them from.
If your business was "NOT" open for business in 2019, then you have absolutely nothing to report concerning the business and will not file a SCH C at all.
All expenses incurred "before" the business is "open for business" are start-up expenses. They get claimed as start up expenses in the first year the buiness is actually "open for business". It does not matter in what tax year those startup expenses were incurred either. But you can't deduct startup expenses until the first tax year the business is actually "open for business".
