How do you make friends when you do believe on god?

The same way as anyone does. My friends and acquaintances seldom discuss religion, and I'm only aware of one who is a full-on atheist, and we do not discuss that with each other. Real friendships are not based on shared ideology, but shared love and concern and being consistently supportive.

Be a good friend without regard to ideology, keep things light and fun.

Friendship is also not entirely rational. One of my best friends, although personally areligious, has a wife who is deeply involved in the Salvation Army church, and is firmly in the Republican camp (although he doesn't understand that the GOP left him in the dust some time ago). His interest in me is that I'm respectful to him and we happen to share the same birthday (though not birth year) and I'm the one person in that particular group who doesn't have to be constantly reminded that it's my turn in a card game because I'm too busy running my mouth. Also I've been to his apartment and fixed his tech for him. I'm okay in his book, even though I'm a godless bastard. He's okay in mine even though he's politically ignorant and inadvertently enabling Trumpism.

That's the way these things work. Friendships involve Other People and you have to get over yourself and your desire to only interact with people who are exactly like you. A life skill here is learning to focus on what you have in common rather than what you don't. See others as human even if they disagree with you or are willfully ignorant in some ways.

Joining Agnostic.com is a great way to start lol.

The same way you make friends when you do. Say hello, be friendly, be honest, avoid talking about religion and politics until you know them better. Finding people with similar interests is always a good way to start.