Inferno is the easiest of the Comedy's canticas to enter, but it asks for help. The poem is short, a little over 4,700 lines, and has a clear plot, a descent with condemned souls who speak; the difficulty lies in the references. Dante uses names of Florence, of mythology and of the Bible without explaining them, and each canto has about 140 lines of linked rhyme.
The structure helps. There are 34 cantos, grouped by circles, and the order is the one Virgil explains in Canto XI, so the reader always knows which sin he is in. The most quoted cantos, the gate (III), Francesca (V), Farinata (X), Ulysses (XXVI) and Ugolino (XXXIII), are narratives, with characters and dialogue, and are read as scenes.
What makes it harder are the references to people of Florence and of thirteenth-century Italy, of which the ordinary reader knows nothing: Guelphs and Ghibellines, Whites and Blacks, the popes Boniface VIII and Nicholas III. With a commentary alongside, the problem lessens. The language also weighs: the original is in archaic Tuscan, in terza rima, and any verse translation exchanges decisive words to keep the rhyme.
For those who are beginning, Canto I gives the whole frame, and Canto V shows the tone. The poem itself warns, in Canto IX, that there is a teaching hidden beneath the veil of the verses: reading slowly is rewarded.