Add gelatine in a cup to that add the 1/4 cup water and mix well and let them dissolve for 5 minutes.
Make mango puree from the mangoes measure and keep.
Add this to mixer jar with sugar and grind this to a smooth puree without any lumps.
Remove this in a bowl and keep.
Now add gelatine mixture to a pan heat up till it makes a clear solution.
Add this clear liquid to the mango puree and beat well to combine nicely,then switch off and mix lemon juice with it and stir well.
In-between you can grease the suitable moulds with very little oil and keep.
Pour this to suitable moulds to set.
Refrigerate till it sets or leave overnight
Notes
If you are not using gelatin then you can use agar-agar.
You can use sugar according to taste depending upon mango sweetness.
This jelly should be refrigerated and does not set on its own like agar-agar.