So you need to have a setup like this hooked up to the tick event to increase 50 points per second.
You need to multiply the value you want per second by Delta Seconds. Delta Seconds gives you the time between tick events. Delta Seconds can change based off of performance, which is why it is an auto computed variable to keep things in line.
Also, be sure to hit the eyeball icon next to your Total Score variable on the left side of your blueprint screen. This will make your variable visible in the editor when you have the blueprint selected.
The default value will not change while the game plays, it is a default value. So once you hit play, hit F1 to gain control of your mouse and select your blueprint from the details panel, you should be able to see your score going up steadily at a rate of 50 points over the course of a second.
If you are wanting to have it tick 0,50,100,150 you could use a timer, or do the same thing as above to make your own custom timer, check to see if it is above a given value (which you know you are incrementing per second) then use a branch to trigger an increase of 50 to the score and reset your custom timer to 0.