If you were fired due to performance issues, how can you rectify this when applying to other jobs and getting interviews?
Unless they ask directly why you left, don't bring it up. If they do ask directly you should talk about how you plan to or have already improve the aspects of your performance that led to you being fired. This can be use of organization tools for time management, improvement of skills through classes or reading, got a vehicle to consistantly get to work on time, etc. Just make sure that any claims you make are true, that you did in fact make an effort to rectify the issue.
Explain it by acknowledging it was an event in your career and express to the interviewer what you know you could have done better. You can say something to the effect of "Yes, I was terminated for performance reasons. What I learned from it is (fill in the blank) and since then I've done (fill in the blank) to improve my performance in that area." You want to show you've taken measurable and identifiable efforts to correct the performance issue which you were fired for. Turn a set back into a growth opportunity. Hiring managers want to see that you're committed to growing and developing yourself. Mistakes happen and terminations/lay off can be inevitable at times. But what matters is what you've made of the situation. Every event in life, good or bad, is an opportunity to grow.