Start with clean containers
Vegetables can be packed into glass jars, or plastic containers to ferment, or you can use a fermentation pot if you have one. These need to seal 100% so they don’t allow any contaminants in, eg from the air.
When using glass jars, sterilise them by putting them through your dishwasher on a hot cycle. Alternatively give clean jars 10 minutes in a hot oven (200°C) or boil them in water for 10 minutes. Leave them to cool completely.