Here is an itemised list of what can be expected, based upon the  applicable Federal laws, which are cited at the end of this article:

• US citizens and entities will be prohibited from engaging in any financial transactions with the government of Venezuela without a specific license from OFAC.
  

• There will be special processing procedures for Venezuelan national seeking a visa to enter the United States. Specifically, there will be no non-immigrant visas issued to any Venezuelan without special agency approval at the highest level. Travel to the US may thus be effectively terminated.
  

• Sovereign Immunity is waived, which permits families and next of kin of terrorist victims to bring civil actions for damages, in US District Court, against the government of Venezuela.
  

• Imports of goods from Venezuela lose any duty-free exemption that they previously enjoyed.
  

• All tax credits for income earned in Venezuela will be thereafter denied.
  

• Loans to Venezuela or its institutions or agencies, or other borrowers from international non-governmental organisations will be opposed by the United States.
  

• Any Venezuelan government-controlled companies will be prohibited from participating in any US Department of Defence contracts that exceed $100,000 .
  

• A ban upon the export of arms and arms-related products to Venezuela.
  

• Severe limitation upon dual-use exports from the US to Venezuela. Dual-use products have both civilian and military applications. There is a 30-day advance notification period where the US Congress is advised of the proposed export.
  

• Total restrictions upon US economic assistance to Venezuela.
  

• Venezuelan financial institutions, which will themselves be the subject of OFAC sanctions at the same time, will also pose a problem, as their US correspondent accounts, their window into the US financial structure, will end up being closed. How will Venezuelans purchase goods and services from US companies?

What I have listed above is a rudimentary forecast of what can be expected after designation; additional sanctions may also be imposed. For your specific questions, you are advised to seek the counsel of a competent legal professional. Though limited to the US, financial institutions in other countries avoid sanctioned countries, due to the possibility that they may themselves be sanctioned, or lose access to US financial markets, by trading with a sanctioned country. it therefore becomes a de facto global sanction.
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For further reading; Readers wishing to review the original authorities:
Export Administration Act of 1979 ( 50 USC App. 2405(j).
Arms Control Export Control Act (22 USC 2780).
Foreign Operations Export Financing and Related Programmes Appropriation Act of 2005 (PL. 93-618).
Trade Act of 1974 ( 19 USC 2462).
Foreign Assistance Act of 1961 (22 USC 2371).
Enhanced Border Security and Visa Reform Act of 2002, section 306. (P.L. 107-173).