It's a complicated class for a first-level player, just because there is much errata to know and class abilities to understand. I'd suggest playing a pre-built sheet, or something else.
Here is the Ultimate Magic FAQ that contains some helpful stuff for Synths.
My honest advice? Play another class. Vivisecionist or Shapechanging Ranger might suit you far better, as you'll find one of the biggest headaches of playing a Synthesist is not only keeping track of all the rules and restrictions yourself, but explaining it to everyone at the table as well. It's a class that works like a Fighter but needs to be planned and thought out as if playing a Wizard.
That said, far be it for me to tell you what you should and shouldn't do. Just so long as you understand just what kind of pit you're getting into.
GL and HF
I'm looking to possibly play a synthesis summoner and would like to base the form around a large bipedal bear who uses a 2h weapon of some sort.
Doesn't have to be the best at anything but I have never played a Synthesis and would like some advice.
Thanks
Well your eidolon can more or less look like whatever you want so it can look like a bipedal bear without issue. Unfortunately you wont be able to take the large evolution untill 8th level, luckily enlarge person is a summoner spell, so you can start as medium and enlarge yourself.
Just take the bipedal base form of the synthesist, you can take the feat martial weapon proficiency (or the evolution of weapon training) to give you access to better 2handed weapons (though you can use simple ones normally so a great club is an option for instance).
Other then that, honestly its really hard to screw up a summoner, make your charisma high, dont worry too much about your physical stats as the eidolons physical stats will replace yours when you are fused. If you want to use a weapon to attack, that frees up evolutions that might have been used on natural attacks to something a bit more interesting, like the skilled evolution or the sense based evolutions.