You can move money in and out of the business at will, just keep track of every transaction. Ideally you'd use an accounting software like QuickBooks or similar. Create a Capital Contributions account and every time you put money into the business checking account record it as a Capital Contribution.
Likewise, if you take money out of the business, it comes from your capital accounts. (You can create a separate Capital Distributions account in your accounting software, or just use a single account for contributions and distributions).
Money coming in and out of those capital accounts is not taxable because you will pay taxes based on net earnings regardless of whether or not you have distributed any profits. So there's no need to make a loan to the company, which would have tax consequences.
To reimburse yourself for purchases already made, submit an expense report to the company. If the company is unfunded right now, you can make a capital contribution to cover current expenses, submit the expense report, and wait until you have some profits before paying out the expense report or making any distributions. Welcome to entrepreneurship.