[Fyron]

Use the search feature of this forum to find info on ringworlds. Check the Newbie FAQ Thread.

Failing that:
1) Research Stellar Manipulation 5 (after Astrophysics 1).
2) Build a number of Space Yard ships (preferably 11).
3) Move the SYSs to the same sector as a star you wish to turn into a RW.
4) Design 3 Starbases. One needs a RW Placement Generator, one needs Hyper-Density Cables, and one needs Gravity Plating (I think thats the name).
5) Build 1 Starbase with the RW Placement Generator, 5 with the Cables, and 5 with the Plating, all in the same sector as the star.

It is best to time their construction so they are all finished on the same turn. This prevents paying maintenance on finished Starbases when waiting for the others to be done. The best way to do this is to place the queue on hold when a particular Starbase is at 1 turn left. Once all are at one turn left, turn them all off of "Hold Queue".

6) Select the Starbase with the RW Placement Generator.

7) Hit the Stellar Manipulation button (or the B key) and select Build Ringworld.

It might be better to build 11 base space yards in the sector of the star and use them to build the Starbases. This frees up the SYSs to other tasks, and gives you 11 orbital BSYs right away when the RW is done. These can build units, ships and bases to defend the newly constructed RW.