Can you explain positron emission and electron capture in nuclear chemistry?

I am doing a project for our nuclear chemistry section and have the topic of positron emission and electron capture. Can anyone explain to me (in simple terms) what these are and do you know any good sites that explain it clearly? Every site I've been to confuses me to no end. Also if you know any good videos I could use to learn it that would be great to because I am a visual learner. Thanks!