Often you may want to plot multiple lines in a line chart in Power BI.
Fortunately this is easy to do and the following step-by-step example shows how to create the following line chart with multiple lines in Power BI:

Let’s jump in!
Step 1: Load the Dataset
First, we will load the following dataset into Power BI that contains information about the total sales made of three different products during various years:

Step 2: Insert the Line Chart
Next, click the Report View icon on the left hand side of the screen:

Then, on the right side of the screen under Visualizations, click the Line chart icon:

An empty line chart will be inserted:

Step 3: Populate the Chart
Next, drag the Year variable under the X-axis label, then drag the Product A, Product B and Product C variables under the Y-axis label:

This will produce the following line chart:

The x-axis displays the year and the y-axis displays the sales by year.
Each of the individual lines represents one of the three products.
Feel free to modify the title of the chart along with the axis titles to make the chart easier to read:

Additional Resources
The following tutorials explain how to perform other common tasks in Power BI:
How to Create a Stacked Column Chart in Power BI
How to Calculate Percent of Total in Power BI
How to Write a Case Statement in Power BI