To make a line graph in Google Sheets, follow these steps:

Step 1: Enter the data

Enter your data in your sheets.
E.g

Step 2: Select the data

The second step after the step 1 is to selecting the data.

Step 3: Click on Insert Chart

Click on "Insert Chart" at top toolbar.

Step 4: Select the line chart.

Select the chart you want to create.

Step 5: Customize

Final step customize your chart such as Color, Point, Legend, Axis and Text.

Step 6: Download

First select your graph and click on three dots.

Finally download your graph as png, svg or pdf format.

OR
You can try line graph maker to create graph easily.