I’ve been attempting to play chun-li and been looking at videos on BnB combos. One of the combos I’ve seen has been c.lk c.lp s.lk into spinning bird kick but I have no clue how to input standing light kick into a spinning bird kick since it’s a charge move? Can someone help please? THANKS 
I have trouble with that move myself. However, according to people who have done it consistently, SBK is a charge move. And the way you do it is that is that from the cr lp/lk into the lk SBK, you have a very tiny windo to put in a neutral st lp/lk before you complete the charge motion into a SBK.
Look the idea is that the game will keep your charge for a certain amount of frames ( currently 6 frames in this version ) even if you let go of the charge.
So you hold back to get your charge then you have 6 frames (1/10 of a second) to let go from down and press upwards plus kick to get a SBK. Now the idea with this combo is that you will be holding down for the cr.LK and cr.LP then you would release the charge and quickly press st.LK and canceling that into the SBK. You are supposed to do the st.LK and to cancel it in this 6 frames window.
There was a trick that @GoofyhanD had shared and that was to press Forward plus the standing light kick/light punch and for some reason that makes it easier to execute for me at least.
If you want to practice it then i would recommend just holding down then pressing neutral st.LK or st.LP then quickly UP + K. When you get a feel or understanding how it works then it becomes much easier to do regularly. It is still a pretty hard trick and one that Capcom made much harder in S2 for no reason.
It is even harder to do this charge trick in SF5 than it was in any SF game in years. The window was 12 frames in S1 so no idea why it became 6 now.