If you're making a T intersection where the two boards meet, I would suggest drilling holes in each board and installing wooden dowels to hold them together. Mark each board where they intersect and drill a few holes in each board that line up with each other.....drill the 3 holes to half the depth of each board and evenly spaced in the joint....around 3" deep... and glue some wooden dowel rod into each hole. Test fit the dowels to make sure they are not too snug and cut them slightly shorter than the full depth of both holes...crimp the outer diameter of the dowels with the teeth of a pliers to create more surface area for the glue to adhere to and make it easier to pound the dowels in place. Home centers or hardware stores, lumber yards, etc..sell wooden dowel rod in various sizes and lengths....something like 1/2" -3/4" thick should do depending on what drill bit size you have and use a good quality wood glue. If you're overlapping the boards at the T intersection, you can use this method too...just drill holes halfway through each board. The trick is getting the holes exactly lined up so measure and mark carefully. You could also screw the boards together with long screws and pilot holes in the first section of wood,,,,drill the start of each hole large enough to countersink the head of the screws...then plug the holes with small dowel plugs and sand/stain as needed. Home centers sell dowel plugs as well for wood craft projects.