Assuming you are a sole proprietor/independent contract (and did not organize your Instacart business as something more complicated), then you must include your instacart income on your tax return along with your other wages and income. You will file a schedule C for your business, listing your gross income and deducting any ordinary and necessary expenses you can prove (probably just mileage). You pay income tax and self-employment tax on the net profit. Here is a blog article to get you started.
https://turbotax.intuit.com/tax-tips/self-employment-taxes/filing-taxes-for-on-demand-food-delivery-...
It is almost always better for a married couple to file jointly, in this case with all your wages, side jobs, dependents, deductions and credits on one tax return. Even if you have a side job.
