OHANA will be a near-infrared long-baseline interferometer. It will be located at the summit of Mauna Kea and will link, by fiber optics, the existing telescopes equipped with adaptive optics into a giant interferometer. OHANA will have baselines up to 4 times longer than VLTI's. The improved resolution will be complementary to VLTI's and will be very well suited to study the star formation processes. Indeed, measuring and understanding the circumstellar environment of young stellar objects (YSOs), especially their accretion disk, is the key to understand the formation of planetary systems. Up to an age of about 10 million years, these disks are thought to be rich enough in dust and gas to host planet formation in their central regions. But this affirmation relies solely on an extrapolation of measurements and models of the outer, tenuous and cold parts of disks where planets cannot form because the measured density is too low. One can therefore rightly wonder how realistic these extrapolations to the central regions are and how secure is the claim that planets are forming around the young solar-like T Tauri stars. The disks' central region, located within a few stellar radii from the center, will become observable by OHANA. In this contribution we will show that OHANA will allow to measure and understand the structure of the accretion disk and differentiate between different models: equatorial vs. magnetospheric accretion; magnetized vs. standard disks, etc. These observations are fundamental to understand the link between the accretion process and the outflow/jet phenomenon frequently observed in these stars.