This line declares that the script is written using version 5 of the Pine Script language.
This line defines a new indicator with the name "Input Symbol". This is the title that will appear on the chart when you add this indicator.
This line creates an input field where the user can select a symbol (a ticker for a stock or other financial instrument). The default value is set to "TSLA" (Tesla). The title of this input field is "Select Symbol".
This line plots the closing price of the currently selected symbol (which defaults to Tesla if the user doesn't select a different one). The plot function is used to draw this value on the chart.