So I dont want to read much of spoilers, but I got the game today, its pretty awwwwwwesome, spent pretty much half the day playing it, mainly goofing off exploring I'm level 8, just joined the companions, did the 2-3 firsts side quest with them, and main quest line I'm on Dragon rising (havent done it yet, want to wait til I get buffed up more).
How I got to white run was pretty random, start of the game, you go to riverwood to talk to Gerdur or whatever, but first person I talked to was the trader in that town, asking me to go take back dragon claw for him, pretty much my first side quest, so I figured Gerdur can wait, I go off, but its pitch fucking dark lol, and frankly speaking, the directions the traders sister gave me was piss poor

So I just go alone on some random direction, see dudes fighting giants, slightly help out, was badass companions (my kind of mofos hehe), but then see some big ass town in horizon (it got lighter out wasnt as oblivious). Havent checked my ingame map by this time, so had no idea where or what this was, but I went in. Got involved alot in the battlehorn-grim-mane's feud (battlehorns are suuuuuuch douches). Got to dragonreach, to give some sword to jarls steward, at this time I was still thinking this is random sidequest or whatever, I should go back to riverwood to talk to Gerdur. But apparently is the main story (Farengar is the douchiest of douches...), and when I did it all, and went back to Gerdur, I couldnt talk to her (or get the free stuff my brother got on his character, damn hehe).
Less babbling, and direct question, how the fuck do I kill the frigging two giants that are guarding the mammuts? I tried when I randomly encountered them doing one of the companion quests (the one with farkas), I died like 7 times in a row lol, tried my magic destruction stuff and every weapon I got, but the mofos just get one clean hit on me (my shield and armour be damned) and I LITTERALLY flew 200 meters up in the air

I'm asking this, because, how the fuck am I supposed to take out dragons if I cant stand a shot against frigging farmer giants lol.
About the Battlehorn and grim-manes stuff, I accepted side quest from the latter family, to retrieve one of them from northwatch keep, I checked where that is on the map and I was gobsmacked lol, I accept too many quests, but this frigging keep was litterally on the faaaar northeast of the map. Does it matter when or which order you do these on? Would take quite a while to say the least to do this one, when I'm still not done with this area's events. I dont have a horse either, except one I took from bandits that died. Cant afford horse, have 2000, and horse costs like 1k+.