Oklahoma City's last-frost date has passed! You can put most of your plants into the garden now, if they've been hardened off. If they've not been hardened off, and you're not sure how, here's my usual process:
Day 1: Put plants outside, in the shade and away from the wind, for about an hour.
Day 2: As above, for a couple hours... and letting them get a few minutes of sun before bringing them in.
Day 3: Put the plants in partial shade for a couple hours, in an area where the wind won't hit them full-blast. (Be careful of that Oklahoma wind!)
Day 4: Similar to day 3, but for about half the day.
Day 5: Similar to day 4, but for about the length of a work-day.
Day 6: Similar to day 5, but with more exposure to to sun and wind.
Day 7: If the plants are doing well, give them full-sun most of the day... but check on them periodically.
Day 8: If all is well, transplant them.
Pay attention to your plants during this process. If they start looking wilty when you put them in the sun, then back off a bit and take smaller steps! And check the forecast before you put them in the ground. Freezes can happen after the last-frost date.