This 'old style' effect still has fans amongst photographers, for various applications, notably portraits amd for creating an 'olde worlde' feel. In Paint.net it's extremely easy to do.
For this task, we'll use the picture of a wedding bride. If you do any wedding photography yoursef, using sepia on some images, particularly the portraits of the bride and groom and family members on their own can be the 'centre piece' of a wedding album.
This picture of the bride is an ideal candidate for sepia tinting, as it is not too dark and has a reasonable range of colour and tones.
Step 2 - Use the Sepia adjustment 
Applying the effect is simple. Just use the menu command: ADJUSTMENTS > SEPIA.
It is a 'one stop' process, there is no opportunity for adjustment of any kind.
The effect is a pleasing one, with a subtlety that you don't get from just a black and white image alone.
Don't forget to use Save As and save this as a new image.
Tip: You might want to try converting the image to Black and White before you apply the Sepia adjustment. See if there is any difference in the overall quality. Conversion in the menu command: ADJUSTMENTS > BLACK AND WHITE.