To care for a String of Turtles (Peperomia prostrata), provide bright, indirect light, water when the topsoil is dry, use a well-draining mix, and maintain a warm environment, avoiding temperatures below 50°F (10°C). 
Here's a more detailed guide:
Light:
String of Turtles thrive in bright, indirect light.
Avoid direct sunlight, especially for smaller or younger plants.
East or west-facing windows offer good indirect light.
If natural light is insufficient, consider using grow lights. 
Watering:
Water when the topsoil feels dry to the touch. 
Allow the soil to dry out somewhat between waterings. 
Overwatering can lead to root rot, so it's better to err on the side of caution and underwater. 
Bottom watering is a good option, allowing the plant to absorb water from the bottom without wetting the leaves. 
Soil:
Use a well-draining potting mix. 
A mix of succulent or cactus mix with perlite or pumice can help with drainage. 
Avoid heavy, clay-based soil that retains too much moisture.