You do have to seal mason jars or canning jars if you want to preserve the food in the mason jars.
If you don't seal the mason jars properly then the food will go bad in the mason jars.
Sealing the mason jars prevents bacteria from growing in the food and makes the food in the mason jars last longer.
You can seal the mason jars with boiling water or by using a mason jar vacuum sealer which is pretty cheap to buy.
If you just seal the mason jar by hand then it may not seal out all the bacteria.
But for something that will not spoil then just sealing the mason jar by hand will be good enough.
To seal mason jars or canning jars with boiling water just place the mason jar into a pot of boiling water for a few minutes.
The boiling water will seal the mason jar.