A moving element can hold in the same time numerous different motions which are all summed together. Think yourself having a bad hangover, every limb trembles uncontrollably say half an inch here and there. But you can still get up and walk to somewhere to get a remedy. 

The trembling continues, but somehow you still succeed at the same time to walk to the wanted direction. Someone can notice from your complex combined motion only the trembling and think "Thanks God, I'm not in that condition!"

The barman in the place where you finally enter notices the familiar customer coming in and says "Welcome, Sir! Nice weather today! How can I help you? The usual?" He ignores your trembling totally, he is interested in only that part of your quite complex motion that brings the paying customer in. If he noticed the trembling he would add "With a straw, I presume!"

Different electromagnetic fields from different radio stations can cause to the same electrons in the same radio antenna several simultaneous movements (=currents)  which all exist at the same time. The total current is the sum of the separate motion components. Cleverly designed circuits filter apart the wanted current generally based on the frequency. If you turn the tuning knob of a radio receiver you generally change the frequency that the receiver accepts. Rest is filtered out.