There's usually an example for each individual thing, which you can copy paste (note though that a number of the TS examples aren't correct and compiler will complain until you fix some error - usually something simple)

eg https://www.pulumi.com/registry/packages/aws/api-docs/rds/instance/#example-usage

For RDS in VPC I did something like this

const vpc = new awsx.ec2.Vpc(...);

const dbSubnetGroup = new aws.rds.SubnetGroup("rds", {
  subnetIds: vpc.privateSubnetIds,
})

const securityGroup = new aws.ec2.SecurityGroup("rds", {
  vpcId: vpc.id,
  ingress: [
    {
      fromPort: 5432,
      toPort: 5432,
      protocol: "tcp",
      description: "Postgres",
      cidrBlocks: [vpc.vpc.cidrBlock],
    },
  ],
});
const postgres = new aws.rds.Instance("postgresdb", {
  //...
  dbSubnetGroupName: dbSubnetGroup.name  vpcSecurityGroupIds: [securityGroup.id],
});

It's python but should be pretty easy to “translate”