Without wanting to sound arrogant, I would say that you should have a look at the forum before posting as there are already millions of threads regarding earning credits.
Anyway, as you've taken the time to post, I will answer. On your profile page, if you hover over Get Credits on top menu then click on Complete Offers, there are loads there. Some are free, most are not. The totally free ones are the surveys (so long as your country allows them!). They can be a pain to do and you can go days without getting anything. But you will eventually so long as you conform to what they want, not what you want to tell them! (You have to lie).
If you don't want to spend money (and many don't - I haven't), then you have to be patient. Learn to play with the clubs you have (you can always upgrade to Starter clubs for free and Tour Starter clubs for 99 credits which you can afford when you get to Pro tier as you get free credits by moving up tiers).
Do some research about which clubs to get; I made a mistake with my first main purchase and wasted 700 credits. Once it's bought you can't take it back for a refund. Well, not striclty true, I could get a refund of 175 credits!
Hope this helps to get you going.