As we discussed in Different Modes and Types of Interpretation, simultaneous interpreting (also called real-time or cabin interpretation) is considered the most challenging form of interpretation to master.
As its name suggests, simultaneous interpreting is when the interpretation is rendered almost at the same time the speaker is speaking. The slight delay is to allow for information gathering so there is context to interpret into. Instead of using notes and your short-term memory, in this instance, you would use your immediate short-term memory. In addition to the inability to take notes, another challenge in simultaneous interpreting is the necessary ability to multitask. You have to listen, comprehend, and analyze an ongoing speech, and then interpret it into a different language while still listening to the speech.
Obviously, you have to be fluent in two or more than two languages and feel comfortable enough to switch quickly back and forth between the languages. More importantly, having a good cultural awareness and understanding is fundamental, since an interpreter has to avoid both misinterpretation and misunderstanding.
In order to improve your real-time interpretation skills, we suggest you practice any time you are free. A good way to start is shadowing a 10 to 20-minute long & structured speech such as TED talks or lecture audios online, then trying to repeat whatever was said in the same languages it was said in the speech. You can adjust the playback speed to make it easy on yourself initially and then try faster and harder subjects. This will train your brain to listen and speak while continuing to listen at the same time. Once you feel comfortable and able to adapt, you can start interpreting the speeches.