Key points 
Your logo is displayed on your public page, your galleries, your emails, and your documents
Without an imported logo, it's your company name that's displayed on your documents
Your legal information (SIRET, VAT) appears on your quotes and invoices
Everything can be modified at any time in your settings
In your page settings (Settings > Appearance > My page) Logo, click on Import an image.
Recommended format: PNG with transparent background (JPG also works)
Your logo is displayed on your public page, your galleries, your emails and your documents
If you don't import a logo, it's your company name that will be written on your quotes and invoices
In your settings, in the Business section ("Business information"), complete your legal and tax information. It appears automatically on your quotes and invoices:
SIRET (14 digits)
Intra-community VAT number (optional, for European exchanges)
Indicate your situation:
Subject to VAT: VAT is calculated on your sales and your documents, at the rate you define
Not subject to VAT: an exemption notice is displayed on your documents (for example "VAT not applicable, art. 293 B of the CGI"). This is the case for sole traders and micro-enterprises.
Logo: public page, galleries, emails, documents
Company name: on your documents (and in place of the logo if you don't add one)
SIRET and VAT: on your quotes and invoices