Lock Schema
Lock Schema is an exposed feature on the interface that will allow the project administrator to freeze the schema state. When the lock is turned on under the Schema menu, no one, including the administrator, can perform changes on the schema objects. The purpose of this lock is to prevent accidental modification to the schema in a project.
The following are the steps to lock the schema for a project:

The following dialog will be prompted when opening any schema related editors:

The schema is locked by Administrator. Do you want to open Fact Editor in read-only mode?

Lock Project
Lock Project prevents other Strategy users from modifying any objects in the locked project in Strategy Developer or Strategy Web. When this lock is turned on under the Administration menu, no one, including the administrator, can perform changes on any objects. Users can execute reports in a locked project, but the report definition that is used is the last definition saved prior to the project being locked.
The following are the steps to lock a project:

The following dialog will be prompted when attempting to open an object in a locked project:

The project is locked because it is being modified by 'Administrator'. Do you want to proceed in read-only mode?

Lock Configuration
When Lock Configuration is enabled under the Administration menu, administrators cannot perform changes on any configuration objects. Thus, no changes can be made to any objects that fall under the Administration icon in Strategy Developer.
The following are the steps to lock configuration for a project source:

The administrator will be prompted with the following dialog when attempting to open a configuration object when the configuration of a project source is locked:

The configuration is locked because it is being modified by 'Administrator'. Do you want to proceed in read-only mode?
From the Administration menu, select Locking - > Unlock Configuration as shown below:

The same options are available in Strategy Workstation 2021, the "Lock Environment Configuration and Project" option is available from "Tools" menu. The Lock schema option is available from Schema blade and lock status.