I am a part owner in an LLC, which reported a loss in 2018. I don't know how to indicate this on my personal tax return
The member responsible for tax matters in the LLC, or the company's accountants, should have mailed you a Schedule K-1, if the LLC reports as a partnership or as an S Corp. The Schedule K-1 information should be entered into TurboTax to transfer your share of profit or loss, capital gain (loss) items, interest, etc. into your Form 1040.