It is not always necessary to play a whole chord to get the effect of a chord. It often works well to take only the most essential notes of the chord and leave the other notes to the bass player and whoever is playing the melody.
Here is a C7 chord. Its notes are C E G Bb.
The second diagram here is the Tritone within the chord. In a dominant 7th chord the tritone is the interval between the 3rd and 7th of the chord. Listen to the effect it produces.
Here are two examples showing the patterns formed by tritones across the fretboard. Memorise these patterns and learn them in all keys.