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1. Okula genellikle yürüyerek giderim. I usually go to school by walking or Usually i walk to school

2. Okula genellikle yürüyerim. yürürüm. Usually i walk to school

3. Okula genellikle yürüyüş yapırım. Its not correct form and not useful for daily Turkish.

There is no difference between 1. and 2. sentences.

3. sentece is not useful and actualy doesnt make a sense.

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 Agree with harp00n, but can add:

"yürüyüş yapmak" is the equivalent to the English "go for a walk" or "take a walk".

We wouldn´t normally say "go for a walk to school" as "go for a walk" is just a general walk, often starting and ending at the same point, maybe for exercise or some other reason.

So Okulda genellikle yürüyüş yaparım would be OK. This would mean "I generally go for a walk at school" and would imply you walk round the school grounds sometime during the day.

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