You want to know how Electronic Invoicing works in SAP Business ByDesign.
SAP Business ByDesign
For Mexico, if the revenue of your company is above the threshold defined by SAT (Servicio de Administración Tributaria), you must issue electronic invoices. You can refer the Help Document Invoice Processing - Mexico for the prerequisites and Process flow in SAP Business ByDesign.
For all other countries you can enable E-Invoicing in SAP Business ByDesign via a partner implementation. You can refer the blog E-Invoicing Integration with SAP ByDesign for more information.
Invoice Processing - Mexico 
Configuration: Communication Arrangement with Business Partner for Electronic Invoices – Mexico 
Configuration: Contractual Agreement with Service Provider for Electronic Invoices
Electronic; Tax to Govt; E-Tax; e-ivoicing, e-invoices, SAT, Servicio de Administración Tributaria, Peppol , KBA , AP-CI-CI-GLO , Cross-Country Extensions , How To