After looking over the large scroll that had the seal etched on to it countless times, looking for any mistakes in the layers of the seal itself, he corrected them once found. Once he was sure he was done he waited until the late evening where no one would be using the training grounds and went to one that was far enough away from the village to test it out.
To keep others from finding out about what he is trying to do, he put down a barrier and security seal around the training field of his choice. Seals if you have enough imagination and the skill to design what they are intended for are bloody amazing. He found himself thankful to Jiraiya. If it wasn't for the pervert of the three Sannin teaching him as much as he could during his two and a half year training trip he wouldn't have been able to come up with this.
Once the security and barrier seals were up, Naruto placed the summoning scroll on the ground and unrolled it. Nodding to himself he placed his hand flat on the middle of the seal and sent a rather small dose of chakra (for him anyway) into it and quickly backed off.
At the time Naruto didn't know the enslavement seal would activate along with the summoning seal. Nor did he know the summoning seal only focused on summoning girls and women from a different dimension to the one Naruto is in; and would continue summoning girls and women from the dimension the first girl came from (although this can be changed in the future). The seal had another function he hadn't noticed when he was creating it or looking it over for mistakes.
The unknown function he unknowingly added would scan the person for any defects, injuries or disfigurements and if it detected any it would automatically 'fix' the persons body seconds after they were brought here.
An example would be if someone had any deformities, or anything that was unnatural to them, then the seal would automatically get rid of it. But if the seal detected it somehow made the person stronger it would still get rid of the deformities but leave behind the benefits it gave them, essentially leaving them the way they were before. Another example is if the person was injured in battle or near death the seal would automatically bring the person back to their top physical condition.
And that is what happened when he activated the summoning seal for the very first time in its creation.