Below are the majorly used SAP IS-U Billing & Invoicing Transaction codes & Tables.
ISU Billing Transaction codes:
        EASIBI - Individual Billing / invoicing / printing at Installation / contract / Contract Account level
        EA00 - Billing / Invoicing / Printing Simulation & Bill Reversal
        EAMABI - Mass Invoice Billing
        EA30/EA31/EA32 - Create / Change / Display Rate
        EA33 - Mass Billing Reversal
        EA35/EA36/EA37 - Create/Change/Display Billing Schema
        EA38 - Mass Billing
        EA05 - Billing and Invoicing outsort release
        EA99 - Variant Program Creation
ISU Invoicing Tcodes:
        EA10 - Mass Invoicing
        EA10_COLL - Collective Invoicing
        EA26 - Batch processing of invoicing
        EA26_COLL - Collective invoice creation in Batch Processing
        EA40 - Display Invoice
Invoice Printing Tcodes:
        EA29 - Printing of invoice
        EA58 - Printing of Collective Invoice
        EA60 - Print individual invoice
        EA64 - Print Collective invoice
Pricing Details:
        EPREI / EPREIH - Pricing Tables
        EA91 - Price Key Maintenance
ISU Billing and invoicing Tables:
        ERCH - Billing Header Table
        ERCHO - OutSorted Bill Documents
        DBERCHZ1/DBERCHZ2/DBERCHZ3 - Billing Line items
        EITR - Billed but not Invoiced Documents
        ERDB - Substitue Documents for COllective invoices
        ERDK - Invoice Header TAble
        EITERDK - Invoiced but not printed Documents
        ERDO - Outsorted Invoice documents
transaction codes (way too many to mention, but here are but a few):
Business Partner: BP
Installation: ES32
Contract: ES30 (not sure though).
Contract account:CAA2
But it would be better to use the CIC0 (Customer Information Center) transaction if you don't know
your way around ISU In CIC you can enter a BP and it will give you an overview of all relevant
objects for this business partner, like contract account, contract, installations, addresses, functional
location, premises etc.
Tables:
BP: BUT000 (and all other BUT* tables).
Contract Account (FKKVK and FKKVKP).
Contract: EVER
Installation: EANL
Premise: EVBS
Address: ADRC
Functional Location: IFLOT