"The things around us are certainly real, but how can we be equally sure about God?"

I see two sides to this. Let's call them the negative and the positive.

NEGATIVE. You take the things around us for granted because you can see and touch them? But how do you know it is not all illusion? How do you know that sense conveys reality? Most folk assume it, but that is no proof; most folk could be wrong, and it has been said that "The majority is always wrong". It has even been suggested that "Reality is an illusion induced by lack of alcohol". And Macbeth says: "Life's but a walking shadow, a poor player that struts and frets his hour upon the stage and then is heard no more. It is a tale told by an idiot, full of sound and fury, signifying nothing".

POSITIVE. A lifetime's pondering has reinforced my conviction that any view of life except the (real) Christian one is stupid. ChristianRelaunch.org explores some of the paths that pondering has followed. For instance, choose "See our response" then "Humanity is a result"; this mentions some pages that I think are relevant to the present question. (No apologies for pointing to the site again. A few years ago I poured an enormous effort into getting all my thoughts into a coherent form, and I myself still refer back to it to clarify my thoughts on various topics!) All this, however, is "mere reasoning", which of course "could be wrong". Everything I think could be wrong. Good thing we are not saved by reasoning!