Connecting the SCD-30 sensor to the Matrix Portal is easy thanks to the STEMMA QT connector system.
Pretty simple. Use the STEMMA QT cable to connect the SCD-30 to the Matrix Portal.
Where to actually place the SCD-30 is sort of up to you and your specific setup. However, you'll want to put a little thought into it to make sure the sensor is properly exposed to the ambient air conditions. Sensirion actually has a document with some guidelines you can read below:
For example, make sure the sensor isn't exposed to direct sunlight. They also have a nice diagram to illustrate suggested placement within an enclosure:
There's also information related to self heating and use in a moving air duct. So give that document a read to help determine where and how best to locate the SCD-30.