Entity structure is the legal form a company is organized under, most commonly a C-corporation or an LLC for a startup, and it determines how the company is taxed, how equity can be issued, and whether it can raise venture funding at all.
Venture investors overwhelmingly require a Delaware C-corp. It's the structure their standard financing documents and fund mandates are built around, and it's the only common startup entity type eligible for QSBS treatment. An LLC is simpler and often better for a company planning to stay bootstrapped or bring on a small number of partners, but converting an LLC to a C-corp later is a real legal and tax event, not a formality.
Getting this right at formation matters more than it seems like it should at the time, since it's expensive, and sometimes impossible, to fully undo later. It's the kind of question worth answering in a calm month rather than after a term sheet has made it urgent.
Add your revenue and website for a full diligence brief, reviewed by a CPA who ran EY's West Coast R&D Tax Credit practice for 13 years.