Is it difficult for a amateur to learn & play this guitar?
There are two aspects of this guitar that distinguish it from others.
- The "Tremolo" Bridge: This allows the player to lower or, if set up to do so, raise the pitch of all the strings. This can lead to the tuning to slip, especially if used intensely. Learning how to use it musically and in a way that keeps it in tune takes time, but it isn't especially difficult. Some players remove the bar and block off the bridge because they don't believe the tremolo effect is worth the cost.
("Tremolo" is varying volume. "Vibrato" is varying pitch. Leo's "Synchronized Tremolo" is vibrato, and the effect built into the Vibrolux is tremolo. We keep using the wrong terms for historic reasons but should probably stop.)
- The Five-Way Pickup Switch: The Stratocaster has three pickups, and since the late 1970s come default with a five-way switch, which allows not only neck, middle and bridge pickups, but the combination of neck-and-middle and middle-and-bridge settings. Some of these positions are associated with some players, songs and genres, and knowing how to get those tones with those switch positions can take effort, but changing those positions do not.
For many reasons, the Stratocaster is designed to be one of the easiest guitars to play. The bridge is highly adjustable to allow you to play comfortably and in tune, the fretboard radius is usually rounded for comfortable chording, and the body is usually a lighter wood and carved to fit the player's body.
The Strat, to me, one of the easiest guitars to play, but that's opinion.
Is Fender Stratocaster electric guitar mostly used by leading guitarists in english pop music songs?
Much of pop music in America and England today is electronic and sample-based, with less guitar. There are a number of guitar builders who take aspects of different instruments and combine them. But the Stratocaster is still a very popular design.