Turn an installed plugin on after its required dependencies are installed and active.

After installation, activation is managed from the plugin’s controls in the Plugin Manager.
An installed plugin is present in TruCMS but can remain inactive. Activate makes TruCMS load the plugin, which is when its administration menus, settings, scheduled behavior, or public features can become available.
Read the dependency information shown under the plugin. TruCMS prevents activation when a required plugin is missing, inactive, or does not satisfy the required version. This is particularly important for the payment add-ons: PayPal, Stripe, Mollie, and Braintree extend TruPayments, so the payment layer must be available first.
Different plugins contribute different parts of the product. Booking adds appointment and service management, TruCommerce adds store operations, TruPayments adds payment management, and gateway add-ons add payment-provider configuration. Activation does not automatically complete those business settings.
Configure from the feature’s own section
After activation, follow the module documentation instead of looking for everything under Core Settings. Booking settings live under Booking, TruCommerce settings under TruCommerce, and payment settings under TruPayments.
Check the dependency message first. Also remember that plugin management actions are permission-controlled; an account can be allowed to view plugins without being allowed to activate them.