Does domain name affect [SEO]
Yes, to a small degree, but not nearly as much as content nowadays.
To rank highly, the content of your page must match certain criteria as implemented by the search engine listing your page. Here is a link to Google's Webmaster Guidelines to give you a rough idea of the more technical aspects of what they would like your page(s) to look like.
[W]hat if I have only 1 keyword in [the] domain name  or no keyword in domain name[?] [I] a want to start a tech blog, is having "bit" in domain name good/OK?
Yes, that is perfectly acceptable.
As mentioned, the content is what matters most. You may want to research specific key words on Google Trends for popularity, either for inclusion in your site name/tags or, more usefully, for target topics you may wish to write about.
[What are the SEO] effects of having [a particular gTLD/ccTLD?]
If you are producing content for a particular country/language, try to use an appropriate ccTLD (country domain). For instance, if your audience is primarily Swedish and you will be writing articles in Swedish, try to choose a .se (Swedish) domain. This will help your ranking with that audience.
If you are writing something that will be read by a larger audience than one country, or simply wish to have a "wider" gTLD (generic domain), you can use .com, .net, .org, etc. Note that there are a lot more gTLDs now (ex. .ninja .eat, .xyz ...). However, at least with Google, the exact gTLD shouldn't matter much. That is, they should ideally have no impact, positive or negative, on the SEO ranking of your website.
You can find a few more details on Google's policy in this July 2015 blog post.
As a suggestion, try to pick something that resonates with your readers. Though taken apparently, something like "techbit.com" might convey quick articles on tech topics and produce the proper connotations with "tech" and "bit" (the latter having an obvious double implication).
You may also consider what the user expects to see for a gTLD. A commercial, coporate website might not want to use a .org, for example. Wikipedia has a list of the currently available ccTLD/gTLDs. Anything listed in the ICANN section in blue should be available (depending on your registrar, of course, whom will have the final list of gTLDs you can choose from).
You may also want to think about advertising. For instance, here is a quick summary of the performance of newer vs. more traditional gTLDs with Google AdWords. In particular, this article basically says that running a Google AdWords campaign on a newer gTLD (e.g. .ninja) is likely to produce similar conversions as running an AdWords campaign on a .com domain, but perhaps be somewhat cheaper.