Build and run not showing up
Im using the Unity version 2017.3.1f1
Need a solution thanks in advance
You are in Export mode. Notice how left button also changes from Build to Export when in export mode too. That is used to export your Unity project to Android project which can be opened with IDE's like Eclipse and Android Studio then built with them.
If you want to build and run the project from Unity, uncheck the Export Project checkbox and the Build And Run button should be enabled again.