Born in Germany, Tosun started his career rising through the ranks at Eintracht Frankfurt, playing for 13 years at various youth levels.
Everton's official website shared a quoted from Tosun on his transfer, "It feels great to be an Everton player", he told EvertonTV. "I'm really excited to work with my new team-mates because Everton has really big names, big players".
The Everton manager said on Thursday, "I think it is personal terms, [that] is the final stage".
"I bring my skills here and everybody is going to see what kind of player I am", he said.
During his time at Besiktas, Tosun has played alongside the likes of former Premier League striker Demba Ba and former Bayern Munich man Mario Gomez.
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"The Premier League is a strong league, I know that, so my own physical strength will help me".
"Also, I can use both my left and my right foot very well and don't have a preference, which is a definite advantage". I'm excited to play with them and to learn from them as well, players like Wayne Rooney and the very good creative players we have here, too.
"I need more goals in the side than what we have at the moment". I hope they can make a lot of assists for me!
"The situation has dragged on for a period of time, they've finished just before Christmas so there has been a period where he has not done any training.we would be cautious but it is not impossible to get him in the squad on the bench".
We are not quite a week into the January transfer window, but it already appears that there will be one out and another in at Goodison Park, and the activity is unlikely to end there for Everton.
The 63-year-old added: "Look, there is going to be a massive pressure on him if we do clinch the signing that he is successful straight away which I'm cautious about".