The modules tab/menu in SAP Business One contains the following modules:

SAP Business One Main Menu: Modules Tab

Administration
Contains the basic system settings for currency exchange rates, system setup, and authorizations, as well as settings for online alerts, and data import/export functions.

SAP Business One Administration Module Menu

Financials
Manages all your accounting data and chart of accounts, general ledger, current accounting posting, and reporting. In addition, you can define budgets and profit centers for better management of company revenues and expenses.

SAP Business One Financials Module Menu

Sales Opportunities
Helps the sales employees to manage their sales opportunities and enables you to analyze your sales information. It also includes opportunity forecast reports, won opportunities, an opportunities pipeline, and a dynamic display of sales stages.

SAP Business One Sales Opportunities Module Menu

Sales – A/R
Handles all aspects of the sales process, from entering sales quotations, sales orders and deliveries, to issuing customer invoices and returns. In addition, you can draw base documents to target documents, or send letters to customers with open debts.

SAP Business One Sales A/R Module Menu

Purchasing – A/P
Lets you manage all your vendor transactions. You can map the entire buying process, from purchase orders to vendor invoicing. Companies that import goods can use the landed costs functionality to calculate the purchase prices of their imported items, including customs, transport and insurance, fees, taxes, and other landed costs.

SAP Business One Purchasing A/P Module Menu

Business Partners
Stores the master data for all your business partners, including relevant information about customers, dealers, vendors, and leads. In addition, you can store information about business partner activities, as well as data for sales volume forecasts.

SAP Business One Business Partners Module Menu

Banking
Handles the full range of monetary transactions. In addition, you can use Payment Engine to process automatic payments.

SAP Business One Banking Module Menu

Inventory
Manages your inventory, including warehouse inventory, price lists, special pricing agreements, alternative items, and warehouse transactions, as well as the pricing and packaging process, and batches and serial number management.

SAP Business One Inventory Module Menu

Production
Enables you to handle bills of material and production orders.

SAP Business One Production Module Menu

MRP (Material Requirements Planning)
Effectively manages your material requirements in the manufacturing process. A planning wizard helps you define planning scenarios that consider existing inventory, sales orders, purchase orders, production orders, and forecasts, to create material ordering recommendations that enable you to fulfill your commitments to your customers.

SAP Business One MRP Module Menu

Service
Manages interaction between service representatives and customers. It enables you to enter and maintain information about service contracts, items and serial numbers, customer complaints and inquiries, as well as perform numerous related functions. Each time a customer reports a problem, you log it in by opening a service call.

SAP Business One Service Module Menu

Human Resources
Maintains information on company employees and enables you to perform numerous related functions. It provides staff management capabilities, including employee details, contact information, and absence reports.

SAP Business One Human Resources Module Menu

Reports
Enables you to compile reports with corporate data and information in exactly the way you want to see it. This includes company internal evaluations, inventory reports, financial reports, and accounting data. In addition to the predefined reports, you can also define individual queries.

SAP Business One Reports Module Menu