Genetic test kits are readily available. It is advisable for you to get tested and your partner, before conceiving a child. The cost is around $500 per person.
You can tests for 150 or up to 1500 diseases. 150 covers the most crucial ones. Everyone will carry some form of disease if you test for a high number of them.
Carrying the potential for a disease is not the same as having a disease. There are no symptoms and you don't have the disease, if you are just a carrier for that disease.
If your partner also carries the same disease, there is an increased chance of your child actually getting the disease and having symptoms.
It is advised to avoid having children with that partner or use a sperm or egg donor who does not carry the disease.
Speak with your doctor and / or a geneticist as some diseases, if carried, are still to be avoided or risks must be assessed. They will also help you assess risk.