As an introduction to systems of equations, you could use the desmos activity to help students understand solutions of systems, practice writing equations, and graphing.  While doing Desmos I suggest using the two students one device format.  This encourages collaboration and discussion.  You can pause the class for discussions and pace students to only view specific screens. 

Link to Desmos Activity - https://teacher.desmos.com/activitybuilder/custom/5807d7306ef115e7053a142a

I would follow up the Desmos Activity with this Illustrative Math Activity where students have to write a system with a specific solution.  This activity would help solidify the concept of solution to a linear equation and solution to a system of equations.  Students could work in pairs and then use a gallery walk to review the various solutions.  

Link to Illustrative Math Activity on Systems - https://tasks.illustrativemathematics.org/content-standards/tasks/1363