The first step of using old plastic bags is to just collect them for a certain period of time until you have a good number. That is important since when they are being melted, they will shrink quite a bit. In order to create one small plastic bowl you should fill one plastic bag with other plastic bags until it is full. That should be enough. It is important the fact that if you shred the bags that will improve the smooth of the bowl.
Second step is to pour half a cup or a whole cup with vegetable oil in an old pot that you will not use anymore for cooking.
This is used so that the plastic does not stick to the pot when it melts. That is really important. So you should use just enough to manage this outcome. The oil also needs to be heated at the stove at approximately medium heat.
Third step is to add the shredded plastic bags to the heated oil and to stir with a spoon made of wood. Another important thing in order to prevent the bags to stick while melting is to stir with a spoon continuously Of course if you think that there will not be enough plastic you can just easily add more bags. That also includes adding a bit more vegetable oil as well.
Forth step is to make sure that the bags are melted enough. That is really important because otherwise they will resist sticking together. What you need is a single smoot melted blob of plastic.
In case if they are lumps in it then you just work them out by using an old fork.
Fifth step is to pour it into the bowl. Just remember that, even if the plastic is not melted enough to pour this is still okay. In order to get it out you should just use the wooden spoon. After you have poured it then you should use the spoon again to give it a shape inside the mold.
Lastly, the sixth step is to let the bowl cool before you use it. If you need it to cool even faster then just put it into a refrigerator. After it has been cooled the plastic bowl should pop out of the mold.
That is how you make something useful out of garbage.