After transferring Pokemon from Pokemon GO to Pokemon Go Park, you can enter the Park in order to interact with the Pokemon you transferred. When you do, you will have the option to try to capture them or to send them to another area of Pokemon Go Park (should you be looking to create a theme). If you choose to try to capture them, you will do so like any other Wild Pokemon Encounter. If a Pokemon Go Park Pokemon flees when you're trying to capture it, it won't leave the park for good. All you must do is simply interact with it again in order to try to capture it once more. You will also receive Experience and Items for catching Pokemon Go Park Pokemon.
The Pokemon you capture in the Pokemon GO Park will have Individual Values and Levels (and thus Combat Points) based upon their Stats in Pokemon GO. Since the Individual Values in Pokemon GO only went up to 15 instead of the usual 31, a Pokemon's IVs will be multiplied by two (plus given an addition point) when transferred to Pokemon Go Park. Their Speed IVs and Natures, however, will be at random since Pokemon GO does not include either of them. A transferred Pokemon's Level will also be coordinated based upon Pokemon GO, with Pokemon from raids being at Level 20 or Level 25 and maxed out Pokemon being a Level 40 and so forth.