Sure, here's a step-by-step guide to set up a Transit Gateway to connect three VPCs in AWS:

Step 1: Create VPCs

1. Create VPC for YGN:
   • Go to the VPC Dashboard.
   • Click on "Create VPC".
   • Name it YGN.
   • IP to 10.1.0.0/16.
   • Create.
2. Create VPC for MDY:
   • Follow the same steps as above.
   • Name it MDY.
   • IP to 10.2.0.0/16.
   • Create.
3. Create VPC for NPT:
   • Follow the same steps as above.
   • Name it NPT-VPC.
   • IP to 10.3.0.0/16.
   • Create.

Step 2: Create Subnets

1. Create Subnet in YGN-VPC:
   • Go to Subnets.
   • Click "Create Subnet".
   • Select YGN.
   • Name it YGN.
   • Create.
2. Create Subnet in MDY-VPC:
   • Follow the same steps as above.
   • Select MDY.
   • Name it MDY.
   • Create.
3. Create Subnet in NPT-VPC:
   • Follow the same steps as above.
   • Select NPT.
   • Name it NPT.
   • Create.

Step 3: Create Internet Gateways

1. Create Internet Gateway for YGN-VPC:

   • Go to Internet Gateways.
   • Click "Create Internet Gateway".
   • Name it YGN.
   • Create.
   • Attach it to YGN.

2. Create Internet Gateway for MDY-VPC:

   • Follow the same steps as above.
   • Name it MDY.
   • Attach it to MDY.

3. Create Internet Gateway for NPT-VPC:

   • Follow the same steps as above.
   • Name it NPT.
   • Attach it to NPT.