refactor(docs): home: write 'usage'

docs/unified-ticketing/usage.md

 # Usage
 
-!!! todo
-    - Write how to add dependency to pom
-    - Write what repo config in pom needed
+## Add as dependency in own project
+
+This library can be used as maven dependency in an own project.
+
+!!! attention
+    As it is not published to maven central,
+    but the GitLab integrated package registry,
+    you must configure an additional repository in your pom.
+
+__repository config:__
+```xml
+<repository>
+    <id>unified-ticketing</id>
+    <url>https://transfer.hft-stuttgart.de/gitlab/api/v4/projects/154/packages/maven</url>
+</repository>
+```
+
+__dependency information:__
+```xml
+<dependency>
+    <groupId>de.hftstuttgart</groupId>
+    <artifactId>unified-ticketing</artifactId>
+    <version>0.1.0</version>
+</dependency>
+```
+
+??? tip "example how your pom should look like"
+    ```xml
+    <project>
+        <!-- [...] -->
+        <dependencies>
+            <!-- [...] -->
+            <dependency>
+                <groupId>de.hftstuttgart</groupId>
+                <artifactId>unified-ticketing</artifactId>
+                <version>0.1.0</version>
+            </dependency>
+        </dependencies>
+        <!-- [...] -->
+        <repositories>
+            <!-- [...] -->
+            <repository>
+                <id>gitlab-maven</id>
+                <url>https://transfer.hft-stuttgart.de/gitlab/api/v4/projects/154/packages/maven</url>
+            </repository>
+        </repositories>
+        <!-- [...] -->
+    </project>
+    ```
+
+## Use in code
+
+There are two central classes: `TicketSystem` and `Ticket`.
+The majority of the library is written with the fluent-api design pattern.
+
+To begin, you'll need an instance of `TicketSystem`.
+This can be done, by calling the builder mechanism or pass a URI with all needed information.
+
+Using this `TicketSystem` object you can search for tickets in the connected space,
+change and save them or create new tickets.
+
+To get full details of the available API, please switch to the [API docs](../api/index.md).
+There you can find information and examples regarding the generic parts of the library,
+as-well as system specific information, e.g. how an URI instantiation string has to look like, etc.